Public Citizen, Inc. v. FERC ( 2021 )


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  •  United States Court of Appeals
    FOR THE DISTRICT OF COLUMBIA CIRCUIT
    Argued May 5, 2021                    Decided August 6, 2021
    No. 20-1156
    PUBLIC CITIZEN, INC.,
    PETITIONER
    v.
    FEDERAL ENERGY REGULATORY COMMISSION,
    RESPONDENT
    DYNEGY MARKETING AND TRADE, LLC, ET AL.,
    INTERVENORS
    On Petition for Review of Orders
    of the Federal Energy Regulatory Commission
    Scott L. Nelson argued the cause for petitioner. With him
    on the briefs was Allison M. Zieve.
    Lona T. Perry, Deputy Solicitor, Federal Energy
    Regulatory Commission, argued the cause for respondent.
    With her on the brief were Matthew R. Christiansen, General
    Counsel, David L. Morenoff, Deputy General Counsel, and
    Robert H. Solomon, Solicitor.
    Richard P. Bress argued the cause for intervenors Vistra
    Corp., et al. With him on the brief were David L. Schwartz and
    Tyce R. Walters.
    2
    Paul W. Hughes and David G. Tewksbury were on the brief
    for amicus curiae Electric Power Supply Association in
    support of respondent.
    Before: TATEL, MILLETT, and PILLARD, Circuit Judges.
    Opinion for the Court filed by Circuit Judge MILLETT.
    MILLETT, Circuit Judge: This case is about the price of
    wholesale electricity—electricity sold from, for example, a
    power plant to a consumer-serving utility company. More
    precisely, this case concerns sales of capacity, which is
    typically a commitment by a power plant to provide electricity
    to a utility in the future. In April 2015, an auction for electrical
    capacity in Illinois produced a striking result. Capacity in
    neighboring regions (from Louisiana up to Minnesota)
    uniformly sold for less than $3.50 per megawatt-day. But in a
    region covering much of Illinois, the auction resulted in
    capacity prices of $150 per megawatt-day—more than 40 times
    the price in those neighboring regions and a nearly ninefold
    increase from the prior year’s price of $16.75.
    After complaints were filed, the Federal Energy
    Regulatory Commission identified numerous problems with
    the existing auction rules. The Commission ordered that the
    auction rules be changed prospectively to prevent unjust and
    unreasonable price spikes. The Commission also launched an
    investigation into potential market manipulation in the 2015
    Auction that lasted more than three years. Nevertheless, the
    Commission later ruled that the identified flaws in the auction
    rules and the high price range those rules established, as well
    as the allegations of market manipulation, did not call into
    question the 2015 Auction or the $150 price it had produced.
    3
    We reject petitioner’s argument that the Commission must
    approve every individual auction price before it goes into
    effect. That is not what the market-based rate scheme requires.
    And we lack the power to review the Commission’s
    discretionary decision to close its investigation into market
    manipulation in the 2015 Auction.
    As for the Commission’s analysis of the 2015 Auction, we
    hold that its decision was arbitrary and capricious. The
    Commission failed to adequately explain why the problems it
    identified in the existing auction rules affecting pricing—
    problems it ordered fixed going forward—did not also affect
    the fairness of the 2015 Auction itself. That omission is
    particularly glaring in light of the starkly anomalous rates that
    the Auction produced. Based on the unwonted record before
    the Commission and the multi-year Commission investigation
    into market manipulation that record prompted, the agency’s
    conclusory and unreasoned decision to sustain the 2015
    Auction rates does not hold up.
    As a result, the petition for review is granted in part and
    denied in part.
    I
    A
    1
    The Federal Power Act, 16 U.S.C. §§ 791a et seq., governs
    both the transmission and the wholesale marketing of
    electricity in interstate commerce, id. § 824(a). The Act
    assigns to the Federal Energy Regulatory Commission the
    responsibility to regulate these activities in the public interest.
    Id. § 824(a), (b).
    4
    Section 205 of the Act, 16 U.S.C. § 824d, mandates that
    “[a]ll rates and charges” within the Commission’s jurisdiction,
    as well as “all rules and regulations” pertaining to those rates
    and charges, must be “just and reasonable[.]” Id. § 824d(a).
    Section 205 also requires all public utilities to “file with the
    Commission * * * all rates and charges for any transmission or
    sale subject to the jurisdiction of the Commission[.]” Id.
    § 824d(c).
    Section 206 of the Act, 16 U.S.C. § 824e, tasks the
    Commission with ensuring that any rates charged are just and
    reasonable. To do so, the Commission can initiate enforcement
    proceedings on its own or upon a complaint from a third party.
    Id. § 824e(a). If the Commission finds that any rate demanded
    by a utility within the Commission’s jurisdiction is “unjust,
    unreasonable, unduly discriminatory or preferential,” then the
    Commission must overturn that rate and impose its own just
    and reasonable rate. Id. The burden of proving an unjust or
    unreasonable rate rests with the party that initiated the
    proceeding—that is, the Commission or the third-party
    complainant. Id. § 824e(b).
    2
    Since the end of the last century, electricity production has
    been increasingly characterized by competitive markets. In
    light of that trend, Congress added a new provision to the
    Federal Power Act in 2005, which is referred to as Section 222
    (codified at 16 U.S.C. § 824v). Entitled “Prohibition of energy
    market manipulation[,]” Section 222 makes it unlawful for any
    entity “to use or employ, in connection with the purchase or
    sale of electric energy or the purchase or sale of transmission
    services subject to the jurisdiction of the Commission, any
    manipulative or deceptive device or contrivance” in
    contravention of Commission rules.                 Id. § 824v(a).
    5
    Section 222, though, does not “create a private right of action.”
    Id. § 824v(b). Instead, enforcement of the prohibition on
    manipulation is assigned exclusively to the Commission. Id.
    Nonetheless, private persons may bring allegations of market
    manipulation to the attention of the Commission by filing a
    complaint under Section 306 of the Act, id. § 825e.
    Implementing the 2005 Act, the Commission has defined
    market manipulation more precisely, modeling it on the
    Securities Exchange Act’s anti-manipulation provisions, 15
    U.S.C. § 78j(b). See Prohibition of Energy Mkt. Manipulation,
    
    114 FERC ¶ 61,047
    , at 5 (Jan. 19, 2006). In that way, the
    prohibition “is not intended to regulate negligent practices or
    corporate mismanagement, but rather to deter or punish fraud
    in wholesale energy markets.” 
    Id. ¶ 5
    . The Commission’s
    regulations make it unlawful, in connection with the purchase
    or sale of electricity or transmission services, to (1) “use or
    employ any device, scheme, or artifice to defraud,” (2) “make
    any untrue statement of a material fact or * * * omit to state a
    material fact necessary in order to make the statements made,
    in the light of the circumstances under which they were made,
    not misleading,” or (3) “engage in any act, practice, or course
    of business that operates or would operate as a fraud or deceit
    upon any entity.” 18 C.F.R. § 1c.2.
    The Commission “defines fraud generally,” so that it
    “include[s] any action, transaction, or conspiracy for the
    purpose of impairing, obstructing or defeating a well-
    functioning market.”          Prohibition of Energy Mkt.
    Manipulation, 
    114 FERC ¶ 61,047
    , at 38–39. The Commission
    has “repeatedly held” that “[a]n entity need not violate a tariff,
    rule or regulation to commit fraud.” Houlian Chen Powhatan
    Energy Fund, 
    151 FERC ¶ 61,179
    , at 58 (May 29, 2015). As
    the Commission has explained, “tariffs cannot be written to
    prohibit all possible fraudulent behavior as ‘[t]he methods and
    6
    techniques of manipulation are limited only by the ingenuity of
    man.’” 
    Id.
     (alteration in original); see also Vitol Inc. &
    Federico Corteggiano, 
    169 FERC ¶ 61070
    , at 32 (Oct. 25,
    2019); In Re Make-Whole Payments & Related Bidding
    Strategies, 
    144 FERC ¶ 61068
    , at 15 n.8 (July 30, 2013)
    (“Many of the Commission’s major enforcement actions under
    Rule 1c (whether litigated or settled) have concerned, either in
    whole or in part, market manipulation in the absence of a
    violation of a specific tariff provision or comparable specific
    market rule.”).
    B
    Before the advent of competitive electricity markets, a
    utility would commonly comply with the Federal Power Act by
    determining the dollar prices it wanted to charge for units of
    electricity, and then filing a schedule of those rates—known as
    a “tariff”—with the Commission. See Morgan Stanley Cap.
    Group Inc. v. Public Util. Dist. No. 1 of Snohomish County,
    
    554 U.S. 527
    , 531 (2008). Those rates generally reflected the
    utility’s costs plus a reasonable rate of return. 
    Id. at 532
    .
    Since 1988, however, the Commission has permitted
    wholesale electricity sellers, such as utilities that own power
    plants, to file “market-based” tariffs instead. Morgan Stanley,
    
    554 U.S. at 537
    ; Market-Based Rates for Wholesale Sales of
    Electric Energy, Capacity and Ancillary Services by Public
    Utilities, 
    72 Fed. Reg. 39,904
    , 39,907 (July 20, 2007)
    (“Market-Based Rates”). Market-based tariffs do not list any
    actual prices for electricity, but instead “simply state that the
    seller will enter into freely negotiated contracts with
    purchasers.” Morgan Stanley, 
    554 U.S. at 537
    .
    This court has held that the Commission’s market-based
    approach is consistent with the Federal Power Act’s
    requirement of “just and reasonable” rates, reasoning that, in a
    7
    “competitive market, where neither buyer nor seller has
    significant market power, it is rational to assume that the terms
    of their voluntary exchange are reasonable, and specifically to
    infer that price is close to marginal cost, such that the seller
    makes only a normal return on its investment.” Tejas Power
    Corp. v. FERC, 
    908 F.2d 998
    , 1004 (D.C. Cir. 1990); see
    Louisiana Energy & Power Auth. v. FERC, 
    141 F.3d 364
    , 365
    (D.C. Cir. 1998); California ex rel. Lockyer v. FERC, 
    383 F.3d 1006
    , 1013 (9th Cir. 2004); see also Elizabethtown Gas Co. v.
    FERC, 
    10 F.3d 866
    , 870 (D.C. Cir. 1993) (approving market-
    based pricing under the Natural Gas Act).
    Even though market-based tariffs do not identify a specific
    price for electricity, the Commission is still statutorily bound
    to ensure that the resulting rates are just and reasonable. To do
    that, the Commission requires assurance for any market-based
    tariff that the seller cannot exercise anticompetitive market
    power. See Blumenthal v. FERC, 
    552 F.3d 875
    , 882 (D.C. Cir.
    2009). More specifically, the Commission has laid out three
    mandatory conditions that must exist for a market-based tariff
    to be approved.
    First, the seller of electricity must demonstrate to the
    Commission’s satisfaction that it and its affiliates either lack,
    or have adequately mitigated, any horizontal or vertical market
    power, and the seller cannot erect any barriers to entry against
    potential competitors. See Market-Based Rates ¶¶ 3, 791, 72
    Fed. Reg. at 39,906, 39,997; 
    18 C.F.R. § 35.37
    ; Morgan
    Stanley, 
    554 U.S. at 537
    ; Louisiana Energy, 
    141 F.3d at 365
    ;
    see also Elizabethtown Gas, 
    10 F.3d at
    870–871. 1
    1
    The Commission has defined “market power” in this context
    as a seller’s ability to “significantly influence price in the market by
    withholding service and excluding competitors for a significant
    8
    Second, some sellers participate in organized regional
    markets for electrical power operated by Regional
    Transmission Organizations (described in more detail below).
    Sellers in those markets “must also abide by additional rules”
    contained in the tariffs filed by the Regional Transmission
    Organizations. Market-Based Rates ¶ 4, 72 Fed. Reg. at
    39,906. Those rules are “designed to help ensure that market
    power cannot be exercised in those organized markets and
    include additional protections,” such as mitigation measures,
    when “appropriate to ensure that prices in those markets are
    just and reasonable.” Id.
    Third, the Commission must continually perform
    “ongoing oversight of market-based rate authorizations and
    market conditions[.]” Market-Based Rates ¶ 5, 72 Fed. Reg. at
    39,906; Blumenthal, 
    552 F.3d at 882
     (approving the
    Commission’s “reasonabl[e] reli[ance] on its continuing
    oversight of the market to guard against potential abuses of
    market power”). This oversight includes reviewing periodic
    reports that sellers and Regional Transmission Organizations
    are required to file, detailing their activities. See Blumenthal,
    
    552 F.3d at
    882–883; 
    18 C.F.R. §§ 35
    .10b, 35.28(g)(4),
    35.37(a)(1), 35.42.
    As relevant here, sellers must file quarterly transaction
    reports containing “(a) a summary of the contractual terms and
    conditions in every effective service agreement for market-
    based power sales; and (b) transaction information for * * *
    market-based power sales during the most recent calendar
    quarter[.]” Refinements to Policies & Procedures for Market-
    Based Rates for Wholesale Sales of Elec. Energy, Capacity &
    period of time.” California Indep. Sys. Operator Corp., 
    126 FERC ¶ 61150
    , at 33 n.123 (Feb. 20, 2009) (quoting Citizens Power & Light
    Corp., 
    48 FERC ¶ 61,210
    , at 7 (Aug. 8, 1989)); Louisiana Energy,
    
    141 F.3d at
    365 n.1.
    9
    Ancillary Servs. by Pub. Utilities, 
    153 FERC ¶ 61,065
    , at 6–7
    (Oct. 16, 2015). Sellers must also notify the Commission any
    time they undergo a change of status “that would reflect a
    departure from the characteristics the Commission relied upon
    in granting market-based rate authority[.]” 
    Id. at 7
    . Certain
    large sellers must file updated market power analyses every
    three years. 
    Id.
    The Commission also requires the Regional Transmission
    Organizations to submit data about their markets on an ongoing
    basis, which helps the Commission “detect anti-competitive or
    manipulative behavior, or ineffective market rules, thereby
    helping to ensure just and reasonable rates.” Enhancement of
    Elec. Market Surveillance & Analysis through Ongoing Elec.
    Delivery of Data from Reg’l Transmission Orgs. & Indep. Sys.
    Operators, 
    139 FERC ¶ 61,053
    , at 2 (April 19, 2012); 
    18 C.F.R. § 35.28
    (g)(4).
    Of course, the mere filing of reports by sellers and
    Regional Transmission Organizations does not itself satisfy the
    Commission’s monitoring obligations. See California ex rel.
    Harris v. FERC, 
    784 F.3d 1267
    , 1273 (9th Cir. 2015). Rather,
    the Commission must actively review those reports and assess
    on an ongoing basis whether the market remains competitive.
    This active supervision enables the Commission to take action
    to “address seller market power or modify rates.” Market-
    Based Rates ¶ 5, 72 Fed. Reg. at 39,906; Montana Consumer
    Counsel v. FERC, 
    659 F.3d 910
    , 919 (9th Cir. 2011)
    (upholding system of market-based tariffs because the
    Commission “has confirmed that it will monitor the data to
    ensure that the reported transactions are consistent with the
    data expected of a competitive, unmanipulated market”).
    For instance, the Commission’s monitoring of transaction
    data may lead it to revoke a seller’s authorization to use market-
    10
    based tariffs if the Commission concludes that the seller may
    have gained market power since its original authorization.
    Market-Based Rates ¶ 5, 72 Fed. Reg. at 39,906. Alternatively,
    the Commission could commence an investigation into
    possible tariff violations or market manipulation, and if it finds
    a violation, the Commission could seek remedies including
    disgorgement, refunds, and civil penalties. Id.
    Whatever enforcement path is chosen, the core
    requirement is that the Commission conduct an “active ongoing
    review” of the performance of market-based tariffs based on
    the filed reports. Harris, 784 F.3d at 1273. The reporting
    requirements—and the continual vigorous monitoring those
    reports enable—are “integral” to a market-based tariff
    “pass[ing] legal muster[.]” Lockyer, 
    383 F.3d at 1015
    ; see also
    Market-Based Rates ¶ 955, 72 Fed. Reg. at 40,017.
    The Commission’s regulations also create mechanisms for
    the public to participate in enforcing these requirements. For
    instance, interested parties may file protests to tariff filings, and
    may seek to intervene in the tariff-approval proceedings before
    the Commission. See 
    18 C.F.R. §§ 35.8
    , 385.211, 385.214. In
    addition, third parties may file complaints with the
    Commission alleging violations of Commission rules or orders.
    
    18 C.F.R. § 385.206
    ; see, e.g., California ex rel. Lockyer, 
    99 FERC ¶ 61247
    , at 14–15 (May 31, 2002) (denying motions to
    dismiss complaint that “challenge[d] sellers’ quarterly
    compliance with the Commission’s reporting requirements”),
    rev’d and remanded on other grounds by Lockyer, 
    383 F.3d at 1018
    ; see also 16 U.S.C. § 824e(a) (permitting complaints
    alleging unjust and unreasonable rates).
    C
    In many parts of the country not dominated by single,
    vertically integrated utilities, the electricity system is managed
    11
    in part by Regional Transmission Organizations and
    Independent System Operators (collectively, “Transmission
    Organizations”). Transmission Organizations serve multiple
    functions, including operating the grid in particular geographic
    areas, constantly balancing supply and demand, and ensuring a
    reliable transmission system. See FERC, ENERGY PRIMER: A
    HANDBOOK FOR ENERGY MARKET BASICS 61 (April 2020),
    https://www.ferc.gov/sites/default/files/2020-06/energy-
    primer-2020_Final.pdf (last accessed July 30, 2021). Most
    relevant here, Transmission Organizations also establish
    markets in which electricity generators can sell their electricity
    wholesale to distributors and other purchasers.
    Some Transmission Organizations also run markets for
    electrical capacity. By way of reminder, in a capacity market,
    distributors of electricity purchase commitments from
    generators to produce set amounts of electricity in the future.
    Advanced Energy Mgmt. All. v. FERC, 
    860 F.3d 656
    , 659 (D.C.
    Cir. 2017). 2 With those commitments in hand, the electricity
    distributor can meet high demands for electricity by calling on
    the generators to produce it when the need arises. 
    Id.
    Purchasing capacity, in other words, ensures that distributors
    can reliably meet predicted peak power demands in an
    upcoming month, season, or year.
    D
    Midcontinent Independent System Operator (“MISO”) is
    a Transmission Organization that, among its other
    responsibilities, conducts annual capacity auctions in portions
    of fifteen states in the Midwest and South.
    2
    Capacity can sometimes also be purchased from consumers
    who promise to forgo consuming a set amount of electricity in the
    future. Advanced Energy Mgmt. Alliance, 860 F.3d at 659.
    12
    For purposes of the auctions, MISO’s operational area is
    divided into nine separate regional “zones.” For each zone,
    MISO determines how much capacity will be required. It also
    determines a “local clearing requirement,” which is “the
    minimum amount of procured capacity that must be physically
    located within the Zone (rather than imported [from another
    Zone or region])” to meet anticipated need. Public Citizen,
    Inc., 
    168 FERC ¶ 61,042
    , at 2 (July 19, 2019) (J.A. 62).
    In the auction, electricity generators offer to sell set
    amounts of capacity at specific prices. Cf. Advanced Energy
    Mgmt. Alliance, 860 F.3d at 659–660. MISO accepts offers,
    beginning with the lowest, until the zone’s capacity
    requirements are met. The price of the last increment of
    capacity needed to meet the zone’s capacity requirements is the
    “auction clearing price” for that zone, and all the capacity for
    that zone is then purchased at that price.
    In addition to those basic rules, MISO applies specific
    rules intended to mitigate the risk that, if the marketplace is
    insufficiently competitive, a seller might exercise market
    power, resulting in an unjust and unreasonable rate. In the
    auction for the 2015-2016 planning year—the year at issue in
    this case—several such rules were in effect.
    First, offers to sell capacity could not exceed the “cost of
    new entry” in a particular zone—that is, the estimated cost of
    building a new power plant to provide capacity in that zone.
    Public Citizen, Inc. ¶ 33 (J.A. 76–77).
    Second, to prevent generators from selling capacity at
    prices substantially higher than the amount they would receive
    from exporting their capacity to another market, MISO
    calculated an “initial reference level” that was “based on the
    estimated opportunity cost” of selling capacity in MISO rather
    than exporting it to a neighboring region. Public Citizen, Inc.
    13
    ¶ 34 (J.A. 77). Specifically, MISO set the initial reference level
    by estimating how much generators could earn by exporting
    capacity to PJM Interconnection, a Transmission Organization
    region that covers portions of thirteen states in the Midwest and
    Mid-Atlantic, rather than selling it to MISO. Simplifying
    somewhat, if an offer exceeded the sum of (i) the initial
    reference level and (ii) ten percent of the cost of new entry—a
    sum known as the “conduct threshold”—the offer was
    automatically lowered to the initial reference level. Id. ¶ 33
    (J.A. 77).
    E
    This case involves a seemingly anomalous result in the
    2015 Auction for MISO’s Zone 4—a zone that covers a large
    portion of Illinois. For that auction, MISO had calculated the
    cost of new entry for Zone 4 at $247.40 per megawatt (MW)-
    day, and the initial reference level (again, based on the
    estimated opportunity cost of not selling energy to PJM) at
    $155.79 per MW-day. Based on these figures, the operating
    rule to ensure fair prices in the auction was that any offer over
    $180.53 per MW-day ($155.79 plus ten percent of $247.40)
    would be automatically reduced to $155.79.
    The Auction took place in April 2015, and when the dust
    settled, the auction clearing price in most of the zones was quite
    uniform. Zones 1, 2, 3, 5, 6, and 7 all cleared at $3.48 per MW-
    day. Similarly, Zones 8 and 9 cleared at $3.29 per MW-day.
    But in Zone 4, the auction clearing price was far higher—$150
    per MW-day. That was not only more than 40 times the price
    set in the other zones, but it was also out of keeping with
    historical rates in Zone 4.          For example, in MISO’s
    immediately preceding 2014-2015 auction, the price in Zone 4
    (along with five other zones) was $16.75 per MW-day.
    Similarly, in MISO’s capacity auction for the 2013-2014
    14
    planning year, the clearing price for Zone 4 (and for the entire
    region) was $1.05 per MW-day.
    The month after the 2015 Auction, four complaints were
    filed with the Commission challenging the exceptionally high
    Zone 4 auction results. The complaints were filed by (1) Public
    Citizen, a public interest and consumer protection organization
    with members in Zone 4; (2) the State of Illinois;
    (3) Southwestern Electric Cooperative, an electric distribution
    cooperative that serves rural consumers in Illinois; and
    (4) Illinois Industrial Energy Consumers, an association of
    large industrial consumers in Illinois.
    Public Citizen, the State of Illinois, and Southwestern
    Electric Cooperative alleged that the 2015 Auction had resulted
    in electricity rates for Zone 4 that were unjust and unreasonable
    in violation of Section 206 of the Federal Power Act, 16 U.S.C.
    § 824e. The State of Illinois explained that the $150 per MW-
    day capacity price would result in an additional $102.1 million
    in total capacity charges in the coming year, and that the
    average residential customer in Zone 4 would pay an additional
    $131 that year.
    Those complainants pointed the finger at Dynegy, a power
    company in Illinois that, in 2013, had purchased four additional
    power plants in Zone 4. The State of Illinois alleged that
    Dynegy had become a “pivotal supplier” for Zone 4, meaning
    that Zone 4 could not meet its local clearing requirement
    without purchasing Dynegy’s capacity. As a result, as the
    auction rules were designed, Dynegy could offer—and would
    receive—any price it wanted in the auction, so long as that
    price was beneath the conduct threshold set by the auction
    rules. In other words, Dynegy could exercise market power
    and garner an unreasonably high price for its electricity
    because the demand for capacity could not be met without it.
    15
    Public Citizen alleged that the unjust and unreasonable
    rates resulted not only from Dynegy’s exercise of market
    power, but also from Dynegy’s “illegal market manipulation of
    the auction through withholding” competitive offers during the
    auction to drive the price up or “other illegal market actions[.]”
    J.A. 152–153. The State of Illinois and Southwestern similarly
    requested that the Commission investigate Dynegy for illegal
    market manipulation.
    Public Citizen separately argued that, notwithstanding any
    filed market-based tariffs, all auction results “must be reviewed
    after-the-fact * * * to determine whether they actually produce
    just and reasonable rates.” J.A. 153.
    Lastly, several complaints attacked the “initial reference
    level” set out in MISO’s tariff as part of the annual auction
    rules. The complaints alleged that the existing reference level
    “[did] not appropriately reflect the opportunity cost of MISO
    capacity resources because it overstate[d] the opportunity to
    sell capacity to PJM.” J.A. 921.
    F
    The Commission responded to these complaints in a series
    of orders, three of which are relevant here.
    1
    In its first order, issued in December 2015, the
    Commission addressed only the portions of the complaints that
    involved prospective challenges to the auction provisions of
    MISO’s tariff. Public Citizen, Inc., 
    153 FERC ¶ 61,385
    , at 3
    (Dec. 31, 2015) (“2015 Order”) (J.A. 910). The Commission
    focused first on those claims because it wanted to act quickly
    “given the limited amount of actionable time prior to the
    2016/2017 Auction[.]” 
    Id.
    16
    The Commission granted the complaints in part and denied
    them in part. As relevant here, the Commission determined
    that “current provisions in the Tariff associated with
    calculating Initial Reference Levels and Local Clearing
    Requirements are no longer just and reasonable for prospective
    application.” 2015 Order ¶ 3 (J.A. 910).
    Recall that the initial reference level reflected the amount
    of money that generators could have earned by selling their
    electricity into PJM, a neighboring market, rather than selling
    it in the MISO auction. The initial reference level helped set
    the upper limit on permissible offers into MISO’s auction,
    based on the assumption that offers below the initial reference
    level were necessarily competitive because a generator could
    have sold its capacity to PJM at that same price.
    But the Commission determined that assumption was no
    longer valid, and so it was no longer “appropriate to continue
    to base the Initial Reference Level * * * on the opportunity
    cost” of not selling capacity into PJM. 2015 Order ¶ 86 (J.A.
    941). Two findings underlay that conclusion.
    First, the Commission found that the rules of the PJM
    marketplace were changing in ways that made it harder to
    compare MISO prices with PJM prices. The Commission had
    recently approved changes to PJM’s capacity market that
    required capacity sellers to be compensated through a more
    complicated pricing model, including additional payments or
    penalties based on performance during peak hours. This
    change meant that, by the 2020-2021 planning year when the
    transition to the new rules would be fully complete, “PJM and
    MISO [would] be procuring different capacity products,” and
    “simply using prices from PJM[] * * * [would] inaccurately
    estimate the opportunity cost of [not] selling capacity into PJM
    in future Planning Years.” 2015 Order ¶ 88 (J.A. 941).
    17
    Second, the Commission concluded that, contrary to
    MISO’s assumption that generators could always sell their
    electricity capacity into PJM, there was neither sufficient
    demand in PJM nor sufficient transmission availability into
    PJM to make those sales possible. The Commission found that,
    in the 2014-2015 planning year, MISO granted only a small
    fraction of requests for transmission services from Zone 4 into
    PJM. See 2015 Order ¶ 89 (J.A. 942) (“[O]nly 200 MW of the
    3,650 MW of monthly firm point-to-point transmission service
    requests were granted.”). Similarly, capacity sales per day
    from MISO into the relevant PJM market were only 64.3 MW
    in 2014-2015 and 12.3 MW in 2015-2016. 
    Id. ¶ 90
    . In other
    words, “in recent years, MISO capacity resources made limited
    sales into the PJM replacement capacity market[.]” 
    Id.
     As a
    whole, this evidence demonstrated that “the opportunity [for
    MISO generators] to make * * * sales [into PJM] is limited due
    to both the limited demand for replacement capacity in PJM
    and the limited ability to attain transmission service from
    MISO to PJM.” 2015 Order ¶ 91.
    Given those findings, the Commission ruled that MISO’s
    calculation of the initial reference level under its tariff was no
    longer just and reasonable. That is because opportunity cost is
    a valid consideration in structuring market prices only if the
    opportunity is “legitimately available to a substantial share of
    the market,” which it was not. 2015 Order ¶ 92 (J.A. 943).
    With no other evidence available to estimate the amount of
    money a generator would be forgoing by selling capacity in
    MISO rather than exporting it elsewhere, the Commission
    ordered that, going forward, the initial reference level must be
    set at $0 per MW-day (rather than the $155.79 initial reference
    level set by MISO for the 2015 Auction). 
    Id. ¶ 93
    .
    The Commission separately determined that MISO’s tariff
    provisions also miscalculated the amount of capacity that
    18
    needed to be procured from power plants located within each
    MISO zone (that is, the local clearing requirement). In essence,
    the Commission held that when MISO calculates the amount
    of capacity that must be generated within a zone to ensure
    reliability, it must consider the consequences for the grid when
    capacity generated locally is exported to other regions, creating
    so-called “counter-flows.” 2015 Order ¶¶ 145–147 (J.A. 963–
    964). Since MISO’s tariff did not properly take these counter-
    flows into consideration in calculating the local clearing
    requirement, the Commission determined that MISO’s
    methodology was unjust and unreasonable, and ordered
    prospective changes to the local clearing requirement
    calculations. 
    Id. ¶¶ 3, 148
    .
    The Commission’s 2015 Order was explicit that the
    complaints’ other arguments about the legality of the 2015
    Auction remained under consideration. 2015 Order ¶ 4 (J.A.
    910). It also advised that the Commission’s Office of
    Enforcement had opened “a formal, non-public investigation
    into whether market manipulation occurred before or during”
    the 2015 Auction. 
    Id.
    2
    Three and a half years later, a divided Commission denied
    the complaints’ remaining challenges to the 2015 Auction.
    The Commission majority ruled that the results of the 2015
    Auction for Zone 4 were “just and reasonable.” Public Citizen,
    Inc., 
    168 FERC ¶ 61,042
    , at 2 (July 19, 2019) (“2019 Order”)
    (J.A. 62). It began by announcing that its investigation into
    potential market manipulation in the 2015 Auction had been
    closed. 
    Id. ¶ 30
     (J.A. 76). The Commission explained that the
    investigation had spanned more than three years, during which
    the Office of Enforcement reviewed over 500,000 pages of
    documents and took seventeen days of testimony from eleven
    19
    witnesses. “Based on a review of the investigation,” the
    Commission found that pricing in the 2015 Auction “did not
    violate the Commission’s regulations regarding market
    manipulation,” and so “no further action [was] appropriate to
    address the allegations of market manipulation raised in the
    complaints.” 
    Id. ¶ 32
    .
    The Commission next rejected the contention that Dynegy
    had exercised market power in the 2015 Auction that caused an
    unjust or unreasonable auction clearing price in Zone 4. The
    only reason given by the Commission for finding no improper
    exercise of market power was that “MISO conducted the
    2015/16 Auction in compliance with the MISO Tariff,” which
    had been “designed to mitigate the exercise of market power
    and result in a just and reasonable rate.” 2019 Order ¶ 84 (J.A.
    104–105). Dynegy’s offers, the Commission observed, were
    “competitive” because they were less than the “conduct
    threshold” of $180.53 per MW-day that was calculated based
    on the initial reference level. 
    Id. ¶ 85
     (J.A. 106). The
    Commission added that “an Auction Clearing Price is not
    unjust and unreasonable because it is higher than expected.”
    
    Id. ¶ 84
     (J.A. 105). The Commission also noted that there was
    no evidence in the record that Dynegy had in any way violated
    the terms of MISO’s tariff.
    Also relevant here, the Commission rejected Public
    Citizen’s argument that the Commission must review
    individual final auction prices across the board for justness and
    reasonableness before those prices could go into effect. 2019
    Order ¶ 89 (J.A. 107). The Commission stated that, while it
    was required to enforce reporting requirements “that enable the
    Commission to evaluate whether rates are just and
    reasonable[,]” it was not required “to make an affirmative
    finding that a rate is just and reasonable before allowing the
    rate to go into effect.” 
    Id.
     The Commission further explained
    20
    that, for purposes of the requirement that sellers file their rates
    with the Commission, “the rate on file with the Commission is
    the Tariff describing the Auction procedures, not the prices that
    may change over time.” 
    Id.
    Then-Commissioner (now Chairman) Glick dissented. In
    his view, “the fact that MISO and the individual market
    participants appear to have followed the relevant tariff
    language does not respond to allegations that the resulting rates
    are unjust and unreasonable as a result of market
    manipulation.” 2019 Order (Glick, Comm’r, dissenting) ¶ 2
    (J.A. 117). He added that the investigation into market
    manipulation had been terminated by the Commission’s
    chairman without a vote by the full Commission. 
    Id. ¶ 1
    . He
    expressed his personal disagreement with that decision, based
    on his belief “that the evidence uncovered to date was more-
    than-sufficient to justify continuing the enforcement process.”
    
    Id. ¶ 4
    . He added that, regardless of the investigation, the
    Commission’s Order “does not provide even the scantest
    reasoning to support its finding that the nearly 1,000 percent
    year-over-year increase in the MISO Zone 4 capacity price had
    nothing to do with market manipulation.” 
    Id. ¶ 5
    . For those
    reasons, he did “not believe we can say with any confidence
    that the 2015 auction was not subject to market manipulation.”
    
    Id. ¶ 6
    .
    3
    Public Citizen sought rehearing of the Commission’s 2019
    Order. It argued that the Commission had failed both “to
    explain the basis for its determination that Dynegy did not
    engage in manipulative practices,” and “to consider whether
    the rates themselves [were] just and reasonable[.]” J.A. 1035.
    In Public Citizen’s view, the Commission had wrongly
    “rel[ied] solely on [the rates] having been established in
    21
    compliance with a previously approved market-based rate-
    setting mechanism[.]” J.A. 1035. In particular, Public Citizen
    pointed out that “the Commission itself ha[d] already
    determined [in its 2015 Order] that continued use of the
    [tariff’s] auction mechanisms used in the 2015/16 auction
    would be unjust and unreasonable[.]” J.A. 1035. Since the
    Commission had “never determined that the tariff’s auction
    provisions themselves were just and reasonable at the time of
    the 2015/16 auction,” it had “failed to explain how it could
    conclude that compliance with those provisions necessarily
    resulted in just and reasonable rates.” J.A. 1036. Public
    Citizen also objected to what it characterized as the
    Commission’s failure to explain its conclusion that Dynegy had
    not committed market manipulation.
    The Commission denied rehearing, again over a dissent
    from then-Commissioner Glick.            Addressing first the
    allegations of market manipulation, the Commission noted that
    it “has discretion on whether and how to explore the possibility
    that market manipulation has occurred.” Public Citizen, Inc.,
    
    170 FERC ¶ 61,227
    , at 6 (March 19, 2020) (“Rehearing
    Order”) (J.A. 130) (citing Heckler v. Chaney, 
    470 U.S. 821
    ,
    831 (1985)). The Commission added that Public Citizen had
    “fail[ed] to accurately articulate and address the definition of
    ‘market manipulation’” in the Act. Id. at 7. And it asserted
    that Public Citizen “ha[d] not met its burden” to show that
    “activity meeting that definition occurred and resulted in rates
    that are unjust and unreasonable.” Id. at 7–8.
    Turning to Public Citizen’s argument that the Commission
    was required to assess whether the auction prices were just and
    reasonable, the Commission held that the argument “rests on a
    fundamental misunderstanding of the Commission’s market-
    based rate program.” Rehearing Order ¶ 16. The Commission
    then concluded that, because Dynegy had received prior
    22
    approval to charge market-based rates from the Commission,
    and because Public Citizen did not allege that Dynegy had
    failed to comply with its reporting obligations, the sales
    “pursuant to Dynegy’s market-based rate tariff at the time of
    the 2015/16 Auction were appropriately made.” Id. ¶ 18.
    Finally, with respect to the justness and reasonableness of
    the 2015 Auction, the Commission rejected Public Citizen’s
    reliance on the Commission’s 2015 Order directing prospective
    changes to MISO’s tariff. The Commission reasoned that its
    2015 Order’s finding that the tariff was unjust and
    unreasonable going forward was based on “changes to the PJM
    capacity market, including future changes to the capacity
    market construct.” Rehearing Order ¶ 22 (J.A. 135–136). The
    Commission reasoned that those changes would only affect the
    opportunity costs for MISO generators “going forward,” so
    they were properly considered only prospectively, and did not
    undermine the Commission’s conclusion that the 2015 Auction
    was based on a “just and reasonable approach to mitigating
    anticompetitive behavior in the MISO capacity market.” Id.
    Dissenting again, Commissioner Glick repeated his
    concern that the Commission “continues to sidestep the key
    question” of whether the 2015 Auction results “were just and
    reasonable in light of the allegations of market manipulation by
    Public Citizen and others.” Rehearing Order (Glick, Comm’r,
    dissenting) ¶ 1 (J.A. 137).
    Public Citizen timely petitioned this court for review of
    both the 2019 Order and the 2020 Rehearing Order.
    II
    We have jurisdiction under the Federal Power Act, 16
    U.S.C. § 825l(b), and review Commission orders under the
    arbitrary and capricious standard. West Deptford Energy, LLC
    23
    v. FERC, 
    766 F.3d 10
    , 17 (D.C. Cir. 2014). To that end, we
    must determine “whether the Commission’s orders examined
    the relevant data and articulated a rational connection between
    the facts found and the choice made.” 
    Id.
     (quotation omitted).
    III
    Public Citizen raises three challenges to the Commission’s
    orders. First, Public Citizen argues that the Commission failed
    to meet its obligation to ensure just and reasonable rates
    because it did not review the prices resulting from the 2015
    Auction before those prices went into effect. Second, Public
    Citizen argues that the Commission was arbitrary and
    capricious in failing to adequately explain its decision to close
    its investigation into whether Dynegy engaged in market
    manipulation.       Third, Public Citizen argues that the
    Commission failed to adequately explain its conclusion that the
    results of the 2015 Auction were just and reasonable.
    We deny Public Citizen’s petition with respect to the first
    two arguments. But we agree that the Commission’s decision
    that the 2015 Auction results were just and reasonable solely
    because the auction process complied with the filed tariff was
    unreasoned on this record. So we grant the petition in part and
    remand to the Commission.
    A
    Public Citizen’s first contention is that Section 205 of the
    Federal Power Act requires the Commission to give its
    affirmative approval to each individual market-based price
    resulting from an auction for electricity or electrical capacity
    before that price can go into effect. That is incorrect.
    Market-based rate regulation is based on the premise that,
    “[i]n a competitive market, where neither buyer nor seller has
    24
    significant market power, * * * the terms of their voluntary
    exchange are reasonable, and * * * [the] price” they negotiate
    will be “close to marginal cost, such that the seller makes only
    a normal return on its investment.” Tejas Power Corp., 
    908 F.2d at 1004
    . On that understanding, we have held that the
    Commission can rationally allow markets to set “just and
    reasonable” prices as long as the Commission takes the
    necessary steps to ensure that market participants cannot wield
    anticompetitive market power. See Blumenthal, 
    552 F.3d at 882
    ; Louisiana Energy, 
    141 F.3d at 365
    ; Elizabethtown Gas,
    
    10 F.3d at
    870–871.
    The Commission has developed a two-part supervisory
    process for ensuring that market rates are just and reasonable,
    and we have held that this process satisfies the Commission’s
    statutory obligations under Section 205 of the Federal Power
    Act. See 16 U.S.C. § 824d. First, before approving the use of
    a market-based tariff, the Commission must make a finding that
    the seller lacks or has adequately mitigated market power.
    Blumenthal, 
    552 F.3d at 882
    . Second, the Commission must
    conduct “continuing oversight” of the market by reviewing the
    mandatory transaction reports filed with it to make sure that
    they corroborate “the continued competitiveness” of the
    market. 
    Id.
     at 882–883.
    This second step is just as critical as the first. See Lockyer,
    
    383 F.3d at 1014
    ; Harris, 784 F.3d at 1275. The Commission
    must review auction results—including prices—as part of its
    obligation to conduct “active ongoing review” of markets and
    market participants. Harris, 784 F.3d at 1273. But in
    conducting that active monitoring, the Commission examines
    auction prices not to determine whether the prices themselves
    are intrinsically just and reasonable, but instead “to ensure that
    the reported transactions are consistent with the data expected
    of a competitive, unmanipulated market.” Montana Consumer
    25
    Counsel, 
    659 F.3d at 919
    ; see Market-Based Rates ¶ 117, 72
    Fed. Reg. at 39,919 (Commission noting that, “as part of our
    ongoing monitoring activities, we examine the [transaction]
    data in an effort to identify whether market prices may indicate
    an exercise of market power”); see also Market-Based Rates
    ¶ 5, 72 Fed. Reg. at 39,906 (affirming that the Commission’s
    review of transactions includes looking out for signs of market
    manipulation). So while prices provide important and relevant
    evidence of the market’s functioning, prices are not themselves
    the object of the Commission’s inquiry.
    This reasonable regulatory regime gives no quarter to
    Public Citizen’s demand that the Commission must examine
    and approve every individual price resulting from every single
    auction to reconfirm that the price is “just and reasonable” in
    its own right. The whole premise of the Commission’s market-
    based system is that a properly competitive market will
    necessarily produce just and reasonable prices.              The
    Commission satisfies its statutory obligations under Section
    205 by giving sellers ex ante approval for market-based pricing
    so long as (1) sellers participating in regional markets obey the
    rules designed to ensure fair and competitive markets, and
    (2) the Commission’s continuing and vigilant monitoring of
    transaction reports verify that the markets work properly when
    the rubber meets the road. Public Citizen’s desire to pile on
    another layer of agency review ignores longstanding precedent
    upholding this regulatory scheme. See Elizabethtown Gas, 
    10 F.3d at 870
     (In a competitive market, the Commission can “rely
    upon market-based prices in lieu of cost-of-service regulation
    to assure a ‘just and reasonable’ result.”); Lockyer, 
    383 F.3d at 1013
     (concluding that market-based tariffs satisfy the
    Federal Power Act given “the dual requirement of an ex ante
    finding of the absence of market power and sufficient post-
    approval reporting requirements”) (emphasis omitted).
    26
    Public Citizen insists that the statute’s multiple references
    to “rates and charges” indicates that sellers must seek
    Commission approval of all auction prices. See 16 U.S.C.
    § 824d(a), (c), (d), (e). 3 But what those references to rates and
    charges require is that they be just and reasonable. See also
    Montana Consumer Counsel, 
    659 F.3d at 921
     (“[T]he ‘rate’
    filed by authorized power wholesalers is the ‘market rate,’ and
    that rate does not ‘change’ even though the prices charged by
    the wholesalers may rise and fall with the market.”); Lockyer,
    
    383 F.3d at 1014
     (“[T]here is nothing inherent in the general
    concept of a market-based tariff that violates the [statute.]”).
    Nothing in the statute dictates the precise methodology the
    Commission must use to ensure the justness and
    reasonableness of rates, whether through individualized review
    or through reviewing and monitoring the process by which
    rates are computed. See Elizabethtown Gas, 
    10 F.3d at
    870
    (citing Mobil Oil Exploration & Producing Se. Inc. v. United
    Distribution Cos., 
    498 U.S. 211
    , 214 (1991)).
    Public Citizen points us to Farmers Union Central
    Exchange v. FERC, 
    734 F.2d 1486
     (D.C. Cir. 1984), but that
    case is of no help to its argument. The Commission’s
    protections of ex ante review, approval of the market design,
    and active post-approval monitoring do not involve “largely
    undocumented reliance on market forces as the principal means
    of rate regulation,” which was the problem in Farmers. 
    Id.
     at
    3
    Paragraph (a) of Section 824(d) requires that all “rates and
    charges” be just and reasonable. 16 U.S.C. § 824d(a). Paragraph (c)
    requires utilities to file schedules of all “rates and charges” with the
    Commission. Id. § 824d(c). Paragraph (d) prohibits utilities from
    changing any “rate” or “charge” without sixty-days’ notice to the
    Commission and the public, “[u]nless the Commission otherwise
    orders[.]” Id. § 824d(d). And paragraph (e) permits the Commission
    to suspend a new “rate” or “charge” under certain circumstances. Id.
    § 824d(e).
    27
    1508; see Blumenthal, 
    552 F.3d at 882
    . TransCanada Power
    Marketing Ltd. v. FERC, 
    811 F.3d 1
    , 4, 13 (D.C. Cir. 2015), is
    also inapt because it did not involve a competitive market-
    based rate system. And Public Citizen, Inc. v. FERC, 
    839 F.3d 1165
     (D.C. Cir. 2016), concerned a settlement agreement that
    specifically required the Commission to perform a “thorough
    review” of actual auction-clearing prices, 
    id. at 1167
    , a
    requirement that has no analogue here.
    For all of those reasons, we reject Public Citizen’s
    argument that the Commission was required under Section 205
    to review the resulting auction prices themselves to determine
    whether they were “just and reasonable.” See 16 U.S.C.
    § 824d.
    B
    Public Citizen next challenges the Commission’s
    conclusory statement that Dynegy did not engage in market
    manipulation, which the Commission made in explaining its
    wholly discretionary decision to close its investigation into
    Dynegy. Because that brief statement was made for the sole
    purpose of explaining the Commission’s decision not to pursue
    an enforcement action, we have no power to review it.
    It has long been settled that “an agency’s decision not to
    prosecute or enforce, whether through civil or criminal process,
    is a decision generally committed to an agency’s absolute
    discretion.” Chaney, 
    470 U.S. at 831
    ; see 
    5 U.S.C. § 701
    (a)(2)
    (excluding from judicial review agency actions “committed to
    agency discretion by law”). In deciding whether to bring an
    enforcement action, an agency must not only determine
    whether a violation of the law occurred, but also whether
    “agency resources are best spent on this violation or another,
    whether the agency is likely to succeed if it acts, whether the
    particular enforcement action requested best fits the agency’s
    28
    overall policies, and, indeed, whether the agency has enough
    resources to undertake the action at all.” Chaney, 
    470 U.S. at 831
    .
    In this case, the Commission conducted a lengthy
    investigation into whether the 2015 Auction’s localized rate
    spike was the product of market manipulation.            The
    Commission’s investigation spanned more than three years,
    produced 500,000 pages of documents, and involved seventeen
    days of testimony from eleven witnesses. 2019 Order ¶ 31
    (J.A. 76). After that, the Commission concluded that “the
    conduct investigated did not violate the Commission’s
    regulations regarding market manipulation[,]” and for that
    reason, “no further action [was] appropriate to address the
    allegations of market manipulation raised in the complaints.”
    Id. ¶ 32 (J.A. 76).
    That type of Commission decision not to pursue further
    investigation or enforcement “is a paradigmatic instance of an
    agency exercising its presumptively nonreviewable
    enforcement discretion.” Baltimore Gas & Elec. Co. v. FERC,
    
    252 F.3d 456
    , 460 (D.C. Cir. 2001). That the Commission
    offered a brief and non-substantive passing word of
    explanation—whether on the question of liability or resource
    limitations—by itself does not open the door to judicial review
    of the non-enforcement decision.
    Public Citizen acknowledges that it can neither “dictate the
    agency’s investigative procedures” nor “seek[] review of an
    exercise of enforcement discretion.” Public Citizen Br. 52. It
    insists instead that it challenges the Commission’s “substantive
    ruling,” in response to complaints, that Dynegy’s conduct did
    not constitute market manipulation. 
    Id.
     The Commission’s
    enforcement decision, Public Citizen says, “rested entirely on
    29
    this resolution of the merits of the claim[,]” and “not on the
    exercise of prosecutorial discretion.” 
    Id.
    But the exercise of prosecutorial discretion is not
    infrequently informed by the agency’s view of the merits—
    whether a violation took place, or whether it could be proved.
    See Chaney, 
    470 U.S. at 831
     (including “whether a violation
    has occurred” among the factors an agency considers in making
    an enforcement decision).
    Nor is there any “law to apply” here. Chaney, 
    470 U.S. at
    834–835.       Under Chaney, the presumption of
    nonreviewability can be defeated if Congress has provided law
    for the court to apply. That would happen, for example, if
    Congress had “indicated an intent to circumscribe agency
    enforcement discretion, and had provided meaningful
    standards for defining the limits of that discretion.” 
    Id. at 834
    .
    That exception does not apply here because nothing in the
    Federal Power Act reins in the Commission’s enforcement
    discretion or provides a meaningful standard for reviewing its
    unexplained conclusion. See 16 U.S.C. § 825e (“[I]t shall be
    the duty of the Commission to investigate the matters
    complained of in such manner and by such means as it shall
    find proper.”); Public Utils. Comm’n of State of Cal. v. FERC,
    
    462 F.3d 1027
    , 1050 (9th Cir. 2006) (“[The Commission]
    enjoys broad discretion in the management of its own [18
    C.F.R.] § 1b prosecutorial investigations.”). 4
    4
    In this way, the Commission’s discretionary enforcement
    decision to close an investigation under Section 306 of the Act, 16
    U.S.C. § 825e, is quite different from the substantive adjudicative
    decisions the Commission must make under Section 206, 16 U.S.C.
    § 824e(a), in response to complaints about whether particular rates
    are just and reasonable.
    30
    In short, under the Federal Power Act, we cannot review
    either the Commission’s discretionary decision to close its
    Section 222 investigation into Dynegy, or the fleeting
    explanation the Commission gave for its action.
    C
    Public Citizen fares better with its argument that the
    Commission failed to explain adequately its conclusion that the
    results of the 2015 Auction for Zone 4 were just and
    reasonable. See 2019 Order ¶ 2. In addressing that issue, the
    Commission fell far short of the type of reasoned explanation
    that the law requires. Most notably, the Commission failed to
    reconcile its prospective holding that the tariff could no longer
    protect against anticompetitive behavior with its conclusion
    that the conspicuously uneven 2015 results—obtained under
    the same flawed tariff terms—were not similarly infected. Nor
    did the Commission provide any explanation for its
    determination that market manipulation did not lead to unjust
    and unreasonable rates.
    1
    In its December 2015 Order, the Commission ruled that
    some of MISO’s tariff provisions—those used to calculate the
    initial reference level and local clearing requirements—were
    “no longer just and reasonable for prospective application[.]”
    2015 Order ¶ 3 (J.A. 910). Most relevant here, the Commission
    determined that it made no sense to estimate MISO sellers’
    opportunity costs by reference to the PJM market because of
    both the demonstrated lack of past demand and transmission
    availability for generators located within MISO to sell their
    energy capacity into PJM, as well as future changes to the PJM
    marketplace. Id. ¶ 92. At bottom, that meant that the tariff’s
    scheme for setting price parameters no longer protected against
    31
    sellers obtaining disproportionate prices through exercises of
    market power or market manipulation.
    Yet in its 2019 Order, the Commission ruled that the
    sharply disparate rates produced in the 2015 Auction by that
    same tariff—applying its no-longer-valid opportunity-cost
    assumptions—were just and reasonable. In doing so, the
    Commission made no effort at all to reconcile its ruling with its
    2015 Order’s findings that the tariff relied on flawed pricing
    assumptions. Not until its rehearing decision did the
    Commission even touch upon the issue. Even then, all the
    Commission said was that the prospective changes ordered in
    the 2015 Order rested exclusively on expected future changes
    to the PJM market. Rehearing Order ¶ 22 (J.A. 135–136).
    Since Dynegy’s auction offers were permissible under the then-
    governing tariff, the Commission added, the results of that
    Auction were necessarily just and reasonable. Id. ¶¶ 22, 23.
    That will not do. The Commission’s 2015 Order listed
    future changes to PJM as only one of the reasons for finding
    the tariff no longer just and reasonable. 2015 Order ¶¶ 87–88
    (J.A. 941–942). The Commission also cited present-day
    problems with the tariff’s assumptions, including the limited
    opportunity, as of 2015, for MISO generators to sell into PJM
    due to both limited demand in PJM and the limited ability to
    obtain transmission service into PJM. Id. ¶¶ 89–92. Those
    latter two determinations rested on evidence and data about
    demand and transmission availability in the 2014-2015 and
    2015-2016 planning years. Id. ¶¶ 89–91. The Commission, in
    short, rested its invalidation of the tariff in material part on
    evidence that, on its face, applies just as much to the 2015
    Auction as to future auction years.
    That apparent flaw directly affected the boundaries within
    which rates were set. For example, without those impugned
    32
    assumptions about opportunity costs, the initial reference level
    in 2015 likely could have been set at $0 per MW-day, just as
    the Commission ordered for future auctions. Instead, based on
    opportunity costs that the Commission’s 2015 Order directly
    called into question, the initial reference level was set at
    $155.79 per MW-day. With an initial reference level of $0,
    generators like Dynegy would have been limited to offering
    capacity at a price of no more than roughly $25 per MW-day,
    and thus would have been unable to submit the 600% higher
    offers that they did in the 2015 Auction. See 2015 Order ¶ 93. 5
    Because this apparent flaw in the 2015 Auction rules led to an
    outlier auction clearing price of $150 per MW-day, the
    Commission was obligated to explain why its opportunity cost
    analysis in the 2015 Order did not require the conclusion that
    the 2015 Auction results—that were predicated on the same
    flawed opportunity-cost assumption—were not unjust and
    unreasonable. 6
    5
    At least, to submit such offers, the companies would have had
    to request a facility-specific reference level and support that request
    with evidence of an individual facility’s distinctive going-forward
    costs.
    6
    We reject intervenor Vistra’s suggestion that Public Citizen
    failed to preserve this issue on rehearing. Public Citizen’s rehearing
    request argued that the Commission’s bare reliance on the 2015
    Auction’s compliance with MISO’s tariff to demonstrate the justness
    and reasonableness of the auction results was undermined by the
    Commission’s own prior determination that the tariff provisions
    were no longer just and reasonable. J.A. 1035–1036 (“That the
    Commission itself has already determined that continued use of the
    auction mechanisms used in the 2015/16 auction would be unjust and
    unreasonable * * * further indicates the unlawfulness of relying
    solely on the auction’s compliance with the then-applicable tariff
    terms[.]”); J.A. 1054 (“[The Commission] failed to consider whether
    33
    The Commission’s orders are similarly devoid of
    explanation as to why the changes to MISO’s local clearing
    requirements dictated in the 2015 Order—that is, the changes
    to MISO’s rules regarding how much capacity had to be
    generated by power plants physically located within Zone 4—
    did not equally implicate the justness and reasonableness of the
    2015 Auction results. Perhaps, as the Commission and Vistra
    (Dynegy’s successor-in-interest) argue, any flaws in the Zone
    4 local clearing requirement would not have affected the
    fairness of the auction. But that argument depends critically on
    the assumption that the tariff’s mitigation provisions, such as
    the initial reference level, were functioning properly. The 2015
    Order takes the air out of that assumption. See 2015 Order
    ¶¶ 85–92 (J.A. 940–943).
    2
    As the Commission agrees, Section 206 allows a
    complainant to allege that market manipulation led to unjust
    and unreasonable rates. See Rehearing Order ¶ 14 (J.A. 131–
    132); Oral Arg. Tr. 35:2–5 (Oral Arg. Rec. 45:38–45:52). Yet
    the Commission’s orders wholly failed to adequately address
    the tariff provisions governing the auction remained just and
    reasonable” despite “the Commission’s determination in December
    2015 that the tariff’s provisions were no longer just and
    reasonable.”). The Commission read the filing that same way
    because it directly responded to the argument that Public Citizen
    made. Cf. Shafer & Freeman Lakes Env’t Conservation Corp. v.
    FERC, 
    992 F.3d 1071
    , 1089 (D.C. Cir. 2021) (finding exhaustion
    where the Commission’s express response “provide[d] strong
    evidence that the * * * rehearing application put the Commission on
    notice of the issue”). Public Citizen cannot be blamed for failing to
    anticipate that the Commission’s response would forget the most
    relevant portions of its own 2015 Order.
    34
    Public Citizen’s allegation that Dynegy’s market manipulation
    produced unjust and unreasonable results in the 2015 Auction.
    Public Citizen’s complaint alleged that market
    manipulation by Dynegy in the form of economic withholding
    had rendered the 2015 Auction results unjust and unreasonable.
    J.A. 151–153. Economic withholding is a type of market
    manipulation in which a utility offers electricity (or capacity)
    at auction at uncompetitively high prices, which artificially
    inflates the market-clearing price. See ENERGY PRIMER 134
    (“Withholding is the removal of supply from the market and is
    one of the oldest forms of commodities manipulation.”).
    Because Dynegy’s acquisition of four new power plants in
    Zone 4 had made it a pivotal supplier of capacity in that zone,
    Dynegy seemingly had the power to set the auction clearing
    price. See Commission Br. 50 (acknowledging that Dynegy
    was a pivotal supplier in the auction); J.A. 145 (Public Citizen
    alleging that Dynegy is “now the dominant provider of capacity
    in the zone”). To that point, Dynegy offered some of its
    capacity in the 2015 Auction at relatively high prices, including
    651 MW at $150 per MW-day and 2,775 MW at $167 per MW-
    day. 2019 Order ¶ 84 (J.A. 105). Public Citizen alleged that
    Dynegy, asserting its new market dominance, “may have
    engaged in intentional capacity withholding to drive auction
    prices from $16.75 to $150.00.” J.A. 145.
    Addressing this allegation for the first time, the
    Commission’s Rehearing Order said that Public Citizen had
    “fail[ed] to accurately articulate and address the definition of
    ‘market manipulation’” under the Federal Power Act, and had
    “not met its burden as a complainant to demonstrate that
    activity meeting that definition occurred and resulted in rates
    that are unjust and [un]reasonable.” Rehearing Order ¶ 14
    (J.A. 131–132).
    35
    On this record, that truncated analysis was inadequate.
    First, Public Citizen more than adequately alleged that
    conduct during the 2015 Auction met the definition of “market
    manipulation” and resulted in unjust and unreasonable rates.
    Public Citizen straightforwardly asserted that “[i]t is illegal for
    an energy market participant to intentionally withhold
    economically viable supply from a generating facility for the
    purpose of inflating prices so it can earn greater profits on sales
    from other remaining generating assets at the higher price
    caused by the withholding.” J.A. 151–152. For this
    proposition it cited the Federal Power Act’s prohibition on
    market manipulation, 16 U.S.C. § 824v(a), and the
    Commission’s implementing regulation, 18 C.F.R. § 1c.2(a),
    which together set out the definition of market manipulation.
    Public Citizen then cited two other proceedings in which,
    according to Public Citizen, the Commission had taken the
    position that “engaging in uneconomic conduct” for the
    purpose of benefiting an entity’s other assets constituted
    market manipulation. J.A. 152.
    For its part, the Commission did not suggest in its orders
    that economic withholding would not constitute illegal market
    manipulation. On its face, economic withholding seems to fit
    within the regulatory definition of market manipulation as
    including any “scheme * * * to defraud,” 18 C.F.R. § 1c.2,
    where “fraud” includes “any action * * * for the purpose of
    impairing, obstructing or defeating a well-functioning
    market[,]” Prohibition of Energy Mkt. Manipulation, 
    114 FERC ¶ 61,047
    , at 38–39. To that point, a 2015 Commission
    staff publication expressly identifies economic withholding as
    a paradigmatic form of prohibited market manipulation under
    the Federal Power Act. See FERC, ENERGY PRIMER: A
    HANDBOOK OF ENERGY MARKET BASICS 129–130 (Nov. 2015)
    (In “[e]conomic withholding * * * the manipulator sets an offer
    36
    price for a needed resource that is so high that the resource will
    not be selected in the market * * * creat[ing] a shortage of
    generation and * * * rais[ing] prices for the benefit of the rest
    of its generation fleet or its financial positions.”). Under these
    circumstances, the Commission’s unexplained reliance on the
    “definition” of market manipulation did not answer Public
    Citizen’s core allegation—that Dynegy may have manipulated
    its auction offers to garner an unreasonably high price.
    Second, as for meeting its burden of proof, Public Citizen
    pointed to the significant evidence before the Commission that
    the auction results were not just and reasonable, and that
    market power or manipulation could have affected the
    outcome. To start, the $150 per MW-day auction clearing
    price, which was 40 times higher than all of the other auction
    clearing prices in zones where Dynegy lacked such market
    dominance, should have raised eyebrows. That price was also
    vastly higher than the Zone 4 clearing prices from prior years.
    See J.A. 63 (clearing price was $16.75 per MW-day in 2014-
    2015, and $1.05 per MW-day in 2013-2014).
    Yet the Commission backhanded the extraordinary price
    spike with the anodyne statement that “an Auction Clearing
    Price is not unjust and unreasonable because it is higher than
    expected.” 2019 Order ¶ 84. Okay. But that does not excuse
    the Commission from grappling with the unusual magnitude of
    the rate increase and its incongruity with other rates within the
    same auction. The Commission also ignored the chronological
    link between the spike and Dynegy’s acquisition of pivotal
    sources of electrical generation within Zone 4. See J.A. 144–
    145, 173; Commission Br. 50; see also Delaware Div. of Pub.
    Advocacy v. FERC, --- F.4th ---, No. 20-1212, 
    2021 WL 2878597
    , at *5 (D.C. Cir. July 9, 2021) (Commission acts
    arbitrarily if it “fail[s] to consider an important aspect of the
    37
    problem”) (quoting Motor Vehicle Mfrs. Ass’n of U.S., Inc. v.
    State Farm Mut. Auto. Ins. Co., 
    463 U.S. 29
    , 43 (1983)).
    On this record, the Commission’s generic assertion that
    “higher” prices alone do not suggest market manipulation
    misses the mark. The clearing price was not just higher, but
    was massively higher than the rates in every other zone, and
    substantial evidence in the record raised the question of a
    market failure. What this record required was nothing more
    and nothing less than a reasoned assessment of the evidence as
    a whole. Yet the Commission did not provide “even the
    scantest reasoning to support its finding” that the massive price
    spike in Zone 4 “had nothing to do with market manipulation.”
    2019 Order (Glick, Commissioner, dissenting) ¶ 5 (J.A. 120).
    Third, instead of weighing the evidence, the Commission’s
    orders repeatedly asserted that the Zone 4 clearing price was
    necessarily just and reasonable “because it resulted from the
    application of MISO’s tariff, which had previously been
    accepted as a just and reasonable approach” to mitigating
    anticompetitive behavior. 2019 Order ¶ 86 (J.A. 106).
    Ah, but “previously been accepted” is exactly the problem.
    In the same year this auction occurred, the Commission found
    that the same tariff could no longer produce just and reasonable
    results. And it did so based in part on empirical grounds that
    applied just as much to the 2015 Auction as to future auctions.
    See 2015 Order ¶¶ 85–92 (J.A. 940–943).
    On top of that, the Commission’s breezy analysis
    overlooks that a market participant could abide by a
    Transmission Organization’s tariff and still manipulate the
    market to produce an unjust or unreasonable rate, as
    Commissioner Glick pointed out in dissent. See 2019 Order
    (Glick, Commissioner, dissenting) ¶ 2 (J.A. 117–118); see also
    Coaltrain Energy, L.P., 
    155 FERC ¶ 61,204
     (May 27, 2016)
    38
    (Commission has “repeatedly held [that] [a]n entity need not
    violate a tariff, rule or regulation to commit fraud.”). To put it
    simply, because the record evidence raised a substantial
    question of whether the tariff provisions had adequately
    mitigated exercises of market power or market manipulation in
    the 2015 Auction, the Commission could not rely reactively on
    compliance with a hobbled tariff as the lodestar of
    competitiveness.
    That is not to say that an extraordinary price spike
    necessarily evidences market manipulation or a malfunctioning
    auction process. The Commission could, on an appropriate
    record, reasonably conclude that a particular price spike, while
    unusual, was not unjust or unreasonable. The problem in this
    case is that the Commission did not do that work. And that
    failure made its order arbitrary and capricious.
    Because the Commission’s orders did not adequately
    explain its conclusion that the 2015 Auction results in Zone 4
    were just and reasonable given the evidentiary record and the
    Commission’s own findings in the 2015 Order, we remand to
    the Commission for further analysis and explanation.
    IV
    For all of those reasons, we grant the petition in part and
    deny it in part, and remand the case to the Commission for
    further proceedings.
    So ordered.