Opinion for the court filed by SILBERMAN, Senior Circuit Judge.
SILBERMAN, Senior Circuit Judge:
These consolidated petitions for review are before us once again. The Maine Public Utilities Commission and the Attorneys General of Connecticut and Massachusetts, representing energy customers, challenged FERC’s approval of a settlement agreement that redesigned New England’s electricity capacity market. Although we rejected most of petitioners’ challenges, we granted their petition regarding the argument that the settlement agreement’s
Mobile-Sierra
provision — which requires FERC to adjudicate challenges to rates resulting from an auction procedure arising out of the settlement agreement under the
Mobile-Sierra
public interest standard — deprived non-settling parties of their rights under the Federal Power Act to challenge rates under the statute’s presumably more searching “just and reasonable” standard.
See Me. Pub. Utils. Comm’n v. FERC,
520 F.3d 464, 477 (D.C.Cir.2008)
(per
curiam). We held that the
Mobile-Sierra
doctrine could not apply to rate challenges brought by non-parties to the settlement agreement.
See id.
The Supreme Court granted
certiorari
on this general issue and reversed.
See NRG Power Mktg., LLC v. Me. Pub. Utils. Comm’n,
— U.S. -, 130 S.Ct. 693, 696-97, — L.Ed.2d -(2010). It identified, however, two questions concerning the
Mobile-Sierra
provision that had been raised before, but not ruled on by, us, and remanded those issues for our consideration.
See id.
at 701. Because the Commission failed to address those issues in the challenged orders, we now remand the orders to FERC.
I
This case has characteristics of a chameleon; it has changed its colors — and its shape — at each stage of the proceedings. As we have previously explained, the basic dispute relates to New England’s electrical capacity market, in which an electricity provider purchases an option to buy electricity from a generator rather than purchasing the electricity directly. That market had been beset by problems, including a supply of capacity that was barely sufficient to meet the region’s demand, and FERC, electricity generators, electricity purchasers, and power customers engaged in several attempts to resolve those issues.
See Devon Power LLC,
115 FERC ¶ 61,-340, at 62,315 (2006). In response to their attempts, FERC required the New England Independent System Operator, the entity operating the electricity transmission system in New England, to develop a new market mechanism that set prices separately by geographic sub-region. Un
der this new mechanism, prices would be highest in the regions with the most severe capacity shortages, encouraging new entries to the max*ket.
See Devon Power LLC,
107 FERC ¶ 61,240, at 62,022 (2004). This mechanism proved extremely controversial, and FERC apparently established settlement procedures to allow all affected parties to develop a different market mechanism. After four months of negotiations, a settlement was reached, which FERC approved.
See Devon Power LLC,
115 FERC at 62,306.
The key feature of the settlement agreement is the Forward Capacity Market, which entails annual auctions that set the rates for electricity “capacity” (the option of buying a quantum of power). In these auctions, which are held three years in advance of when capacity is needed, electricity providers buy capacity at a standard rate, and must purchase enough capacity to maintain the reliability of the electricity grid.
See id.
As noted, the settlement agreement provided that challenges to the resulting auction rates— whether brought by a settling party, a non-settling party, or the Commission— would be “adjudicated under the highly-deferential
Mobile-Sierra
‘public interest’ standard rather than the usual ‘just and reasonable’ standard” of the Federal Power Act.
Me. Pub. Utils. Comm’n,
520 F.3d at 469.
It should be noted that, at the outset of this litigation, it was common ground among all pax-ties that the normal statutory “just and reasonable” standard was a different standard than the “public interest” standard. This belief no doubt was shaped by the eponymous cases of the
Mobile-Sierra
doctrine, in which the Supreme Court addi’essed the Commission’s authority to modify rates set by contract. In
United Gas Pipe Line Co. v. Mobile Gas Service Corp.,
350 U.S. 332, 76 S.Ct. 373, 100 L.Ed. 373 (1956), the Court held that under the Natural Gas Act, a utility could not abrogate a lawful contract with a purchaser merely by filing a new rate. 350 U.S. at 336-37, 76 S.Ct. 373. And in
Federal Power Commission v. Sierra Pacific Power Co.,
350 U.S. 348, 76 S.Ct. 368, 100 L.Ed. 388 (1956), it applied
Mobile
to the Federal Power Act, and confronted the question of how the Commission evaluates when a contract rate is just and reasonable. 350 U.S. at 352-53, 76 S.Ct. 368. The Court held that a utility that had entered into a contract setting rates could not subsequently seek a greater return by asserting the contract rate was inadequate to meet the just and reasonable standard.
See id.
at 354-55, 76 S.Ct. 368. It could only escape that rate if the utility could show the “public interest” was jeopardized — which apparently meant the utility faced something close to insolvency, the rate created an excessive burden for consumex's, or the rate was unduly discriminatory.
See id.
We subsequently extended that hurdle symmetrically to challenges brought by purchasers, in addition to challenges brought by sellers.
See Potomac Elec. Power Co. v. FERC,
210 F.3d 403, 404-05 (D.C.Cir.2000).
It appeared to us that application of the
Mobile-Sierra
doctrine was a form of estoppel,
i.e.,
a contracting party was not at liberty — short of extraordinary circumstances — to avoid its negotiated contract rate. And therefore we framed the
Mobile-Sie'iTa
issue in our px-evious opinion as whether “the Commission [may] approve a settlement agreement that applies the highly-deferential ‘public interest’ standard to rate challenges brought by non-contracting third parties.”
Me. Pub. Utils. Comm’n,
520 F.3d at 477. FERC’s orders had been somewhat ambiguous as to why the Commission decided it could impose the
Mobile-Sierra
standard on non-settling parties. But we found no need to
parse FERC’s various explanations, because we concluded that the Commission could not approve the settlement agreement’s
Mobile-Sierra
clause that bound non-settling parties.
Then, before the Supreme Court, the ground shifted. Three months after we issued our original opinion in this case, the Supreme Court decided
Morgan Stanley Capital Group Inc. v. Public Utility District No.
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Opinion for the court filed by SILBERMAN, Senior Circuit Judge.
SILBERMAN, Senior Circuit Judge:
These consolidated petitions for review are before us once again. The Maine Public Utilities Commission and the Attorneys General of Connecticut and Massachusetts, representing energy customers, challenged FERC’s approval of a settlement agreement that redesigned New England’s electricity capacity market. Although we rejected most of petitioners’ challenges, we granted their petition regarding the argument that the settlement agreement’s
Mobile-Sierra
provision — which requires FERC to adjudicate challenges to rates resulting from an auction procedure arising out of the settlement agreement under the
Mobile-Sierra
public interest standard — deprived non-settling parties of their rights under the Federal Power Act to challenge rates under the statute’s presumably more searching “just and reasonable” standard.
See Me. Pub. Utils. Comm’n v. FERC,
520 F.3d 464, 477 (D.C.Cir.2008)
(per
curiam). We held that the
Mobile-Sierra
doctrine could not apply to rate challenges brought by non-parties to the settlement agreement.
See id.
The Supreme Court granted
certiorari
on this general issue and reversed.
See NRG Power Mktg., LLC v. Me. Pub. Utils. Comm’n,
— U.S. -, 130 S.Ct. 693, 696-97, — L.Ed.2d -(2010). It identified, however, two questions concerning the
Mobile-Sierra
provision that had been raised before, but not ruled on by, us, and remanded those issues for our consideration.
See id.
at 701. Because the Commission failed to address those issues in the challenged orders, we now remand the orders to FERC.
I
This case has characteristics of a chameleon; it has changed its colors — and its shape — at each stage of the proceedings. As we have previously explained, the basic dispute relates to New England’s electrical capacity market, in which an electricity provider purchases an option to buy electricity from a generator rather than purchasing the electricity directly. That market had been beset by problems, including a supply of capacity that was barely sufficient to meet the region’s demand, and FERC, electricity generators, electricity purchasers, and power customers engaged in several attempts to resolve those issues.
See Devon Power LLC,
115 FERC ¶ 61,-340, at 62,315 (2006). In response to their attempts, FERC required the New England Independent System Operator, the entity operating the electricity transmission system in New England, to develop a new market mechanism that set prices separately by geographic sub-region. Un
der this new mechanism, prices would be highest in the regions with the most severe capacity shortages, encouraging new entries to the max*ket.
See Devon Power LLC,
107 FERC ¶ 61,240, at 62,022 (2004). This mechanism proved extremely controversial, and FERC apparently established settlement procedures to allow all affected parties to develop a different market mechanism. After four months of negotiations, a settlement was reached, which FERC approved.
See Devon Power LLC,
115 FERC at 62,306.
The key feature of the settlement agreement is the Forward Capacity Market, which entails annual auctions that set the rates for electricity “capacity” (the option of buying a quantum of power). In these auctions, which are held three years in advance of when capacity is needed, electricity providers buy capacity at a standard rate, and must purchase enough capacity to maintain the reliability of the electricity grid.
See id.
As noted, the settlement agreement provided that challenges to the resulting auction rates— whether brought by a settling party, a non-settling party, or the Commission— would be “adjudicated under the highly-deferential
Mobile-Sierra
‘public interest’ standard rather than the usual ‘just and reasonable’ standard” of the Federal Power Act.
Me. Pub. Utils. Comm’n,
520 F.3d at 469.
It should be noted that, at the outset of this litigation, it was common ground among all pax-ties that the normal statutory “just and reasonable” standard was a different standard than the “public interest” standard. This belief no doubt was shaped by the eponymous cases of the
Mobile-Sierra
doctrine, in which the Supreme Court addi’essed the Commission’s authority to modify rates set by contract. In
United Gas Pipe Line Co. v. Mobile Gas Service Corp.,
350 U.S. 332, 76 S.Ct. 373, 100 L.Ed. 373 (1956), the Court held that under the Natural Gas Act, a utility could not abrogate a lawful contract with a purchaser merely by filing a new rate. 350 U.S. at 336-37, 76 S.Ct. 373. And in
Federal Power Commission v. Sierra Pacific Power Co.,
350 U.S. 348, 76 S.Ct. 368, 100 L.Ed. 388 (1956), it applied
Mobile
to the Federal Power Act, and confronted the question of how the Commission evaluates when a contract rate is just and reasonable. 350 U.S. at 352-53, 76 S.Ct. 368. The Court held that a utility that had entered into a contract setting rates could not subsequently seek a greater return by asserting the contract rate was inadequate to meet the just and reasonable standard.
See id.
at 354-55, 76 S.Ct. 368. It could only escape that rate if the utility could show the “public interest” was jeopardized — which apparently meant the utility faced something close to insolvency, the rate created an excessive burden for consumex's, or the rate was unduly discriminatory.
See id.
We subsequently extended that hurdle symmetrically to challenges brought by purchasers, in addition to challenges brought by sellers.
See Potomac Elec. Power Co. v. FERC,
210 F.3d 403, 404-05 (D.C.Cir.2000).
It appeared to us that application of the
Mobile-Sierra
doctrine was a form of estoppel,
i.e.,
a contracting party was not at liberty — short of extraordinary circumstances — to avoid its negotiated contract rate. And therefore we framed the
Mobile-Sie'iTa
issue in our px-evious opinion as whether “the Commission [may] approve a settlement agreement that applies the highly-deferential ‘public interest’ standard to rate challenges brought by non-contracting third parties.”
Me. Pub. Utils. Comm’n,
520 F.3d at 477. FERC’s orders had been somewhat ambiguous as to why the Commission decided it could impose the
Mobile-Sierra
standard on non-settling parties. But we found no need to
parse FERC’s various explanations, because we concluded that the Commission could not approve the settlement agreement’s
Mobile-Sierra
clause that bound non-settling parties.
Then, before the Supreme Court, the ground shifted. Three months after we issued our original opinion in this case, the Supreme Court decided
Morgan Stanley Capital Group Inc. v. Public Utility District No. 1 of Snohomish County,
554 U.S. 527, 128 S.Ct. 2733, 171 L.Ed.2d 607 (2008), which held that the
Mobile-Sierra
public interest standard was only an application of the just and reasonable standard to contract, not a different standard. 128 S.Ct. at 2740. In light of that decision, the Court took
ceHiorari
in this case to answer a single question: whether
“Mobile-Sierra’s
public-interest standard applies] when a contract rate is challenged by an entity that was not a party to the contract.”
NRG Power Mktg., LLC,
130 S.Ct. at 698 (internal quotation marks omitted). The Court, therefore, shifted the focus of the case from the settlement agreement to the nature of the auction rates resulting from the settlement agreement.
Following the Supreme Court’s lead, the parties presented arguments about whether
Mobile-Sierra
applied only to contract rates. Maine Public Utilities Commission and its allies, respondents before the Supreme Court, squarely contended for the first time (undoubtedly in light of
Morgan Stanley)
that the auction rates were
not
contract rates (a point that they had not specifically made before, except by adopting an argument in an intervenor’s brief). Petitioners before the Supreme Court, who had been intervenors defending the settlement agreement before us, now argued (again surely influenced by
Morgan Stanley)
that the rates
were
contract rates. And FERC, for its part, took a third position: the rates were
not
contract rates, yet it nevertheless had authority to approve the
Mobile-Sierra
clause as a matter of its discretion.
Relying on
Morgan Stanley,
the Supreme Court concluded that the
Mobile-Sierra
doctrine “is not limited to challenges to contract rates brought by contracting parties. It applies, as well, to challenges initiated by third parties.”
NRG Power Mktg., LLC,
130 S.Ct. at 701. And therefore it implicitly, but necessarily, rejected our conclusion that FERC could not approve a
Mobile-Sierra
clause in a settlement agreement that bound non-settling parties. That is, if non-contracting parties are bound to challenge contract rates under
Mobile-Sierra,
it must be that FERC can approve a settlement agreement requiring adjudication of any rates resulting from that settlement agreement under
Mobile-Sierra
if the resultant rates are contract rates. But the Supreme Court’s holding did not resolve this case, because as the parties’ positions before it made clear, there was still an open question about whether the auction rates resulting from the settlement agreement were the type of rates to which
Mobile-Sierra
applied. The Court declined to consider this issue, reasoning that it had been “raised before, but not ruled upon by, the Court of Appeals.”
Id.
The Supreme Court therefore asked us to consider that issue in the first instance.
See id.
The parties now present on remand the same arguments deployed in the Supreme Court.
It is necessary to describe this jurisprudential Kabuki dance to deal both with a jurisdictional issue, as well as with the merits. The intervenors defending the settlement agreement (although not FERC) contend that we lack jurisdiction to consider petitioners’ argument that the auction rates are not contract rates to which
Mobile-Sierra
can apply because petitioners did not make that precise argument before FERC' — only intervenors opposing the settlement did. And our cases are quite clear that generally we do not have jurisdiction under the Federal Power Act to consider an argument not raised by a petitioner
before FERC;
an intervenor cannot fill the jurisdictional gap.
See, e.g., Platte River Whooping Crane Critical Habitat Maint. Trust v. FERC,
876 F.2d 109, 113 (D.C.Cir.1989);
see also
16 U.S.C. § 825i(b).
It would be rather anomalous at this point for us to hold that we lacked jurisdiction to consider the issues the Supreme Court has explicitly remanded to us. Moreover, given the shifts in the parties’ positions — including FERC’s — as well as the unanticipated change in the Supreme Court’s
Mobile-Sierra
jurisprudence, it might be thought overly technical to bar petitioners’ argument. But it is unnecessary to consider these factors. Intervenors, in asserting that petitioners did not raise the precise argument that the auction rates are not contract rates before FERC, are slicing the salami too thinly. After all, petitioners did argue before FERC that the
Mobile-Sierra
provision in the settlement agreement “deprives non-settling parties of their rights under Section 206 of the Federal Power Act,” an argument that applies whether or not the auction rates are regarded as contract rates.
Interestingly, FERC, when presented with intervenors’ more precise formulation that the auction rates were not contract rates, said “[w]e also reject [intervenors’] contention that market rules and tariffs are not contracts to which
Mobile-Sierra
can apply,” yet ambiguously also said that “tariffs have been held to be analogous to contracts.”
Devon Power LLC,
117 FERC ¶ 61,133, at 61,727 (2006). The Commission apparently did not see intervenors’ contention that the auction rates were not contract rates as separate from petitioners’ general challenge to the
Mobile-Sierra
clause because it never actually resolved the former question, which likely explains why FERC did not join the jurisdictional objection.
II
As we noted, the Supreme Court granted
certiorari
to determine whether the
Mobile-Sierra
public interest standard applied to a challenge to contract rates brought by a non-contracting party. And that issue was affected decisively by
Morgan Stanley,
which the Supreme Court decided after we issued our previous opin
ion in this case. A freely-negotiated contract rate, the Court held in
Morgan Stanley,
was presumptive evidence that the rate was just and reasonable because it reflected market forces.
See Morgan Stanley,
128 S.Ct. at 2739-40, 2746-47. Based on that reasoning, the Supreme Court concluded in this case that
Mobile-Sierra
could apply to a rate challenge brought by a non-contracting party.
See NRG Power MUg.,
130 S.Ct. at 701.
We admit to being somewhat uncertain about the implications of the Supreme Court’s opinion in our case because although it states, following
Morgan Stanley,
that the public interest standard is merely an application of the just and reasonable standard,
see id.
at 700, its accurate description of
Sierra
makes clear that there an examination of the disputed rate under the just and reasonable standard would have led the Commission to overturn the rate, where adjudication under the public interest standard would not have,
see id.
at 699. It therefore appears that if the
Mobile-Sierra
doctrine is only an application of the just and reasonable standard — not a separate standard — it is true only at some theoretical level. Be that as it may, since the Supreme Court invigorated the
Mobile-Sierra
doctrine, and remanded for a determination whether the auction rates were protected against attack, either because they are freely-negotiated contract rates or because FERC has discretion to apply
Mobile-Sierra
to non-contract rates, it is obvious that the Court is of the view that the
Mobile-Sierra
public interest standard confers an advantage on a party claiming it applies.
Doctrinal difficulties aside, we turn to the questions the Supreme Court put to us: “[wjhether the rates at issue qualify as ‘contract rates,’ and, if not, whether FERC had discretion to treat them analogously.”
Id.
at 701. FERC’s counsel now concedes flatly that the auction rates are not contract rates, but rather closely resemble a conventional “cost based tariff rate” because during the Forward Capacity Market auction, a capacity buyer is simply assessed a standard market rate. Unlike a typical auction, then, the buyers do not agree to pay a seller a specific price set by a voluntary bid, so therefore no voluntary agreements develop. Nevertheless, FERC’s counsel argues that under the logic of
Morgan Stanley,
the Commission always has discretion to approve a clause that provides protection against an attack on these rates as unjust or unreasonable by imbuing them with the more difficult to challenge “public interest” cloak.
Exercising that discretion is appropriate here, FERC’s counsel believes, because the auction rates “share with freely negotiated contracts certain market based features that tend to assure just and reasonable rates.” Respondent’s Supplemental Brief at 13.
We cannot decide whether FERC’s counsel’s current position is reasonable under the APA because it is certainly obvious — whatever else is confusing about this case — that FERC never articulated
in its orders
a rationale for its discretion to approve a
Mobile-Sierra
clause outside the contract context, or an explanation for exercising that discretion here.
See Fed. Power Comm’n v. Texaco Inc.,
417 U.S. 380, 397, 94 S.Ct. 2315, 41 L.Ed.2d 141 (1974) (“[W]e cannot ‘accept counsel’s
post hoc
rationalizations for agency action ....’” (quoting
Burlington Truck Lines, Inc. v. United States,
371 U.S. 156, 168-69, 83 S.Ct. 239, 9 L.Ed.2d 207 (1962))). However FERC justifies its decision to approve the
Mobile-Sierra
clause, FERC must explain why, if the auction
rates are not contract rates, they are entitled to
Mobile-Sierra
treatment. Just how do the auction rates reflect market conditions similar to freely-negotiated contract rates? Or does FERC base its asserted discretion on some other ground?
For the foregoing reasons, FERC’s orders approving the settlement agreement’s
Mobile-Sierra
provision are remanded for further proceedings.
So ordered.