Opinion for the Court filed by Circuit Judge SENTELLE.
Great Lakes, a pipeline company, Trans-Canada, its principal customer, and other interested firms petition for review of several orders of the Federal Energy Regulatory Commission (the “Commission”):
Great Lakes Gas Transmission L.P.,
We hold that the Commission employed a standard to judge the permissibility of rolled-in rates that neither accords with the Commission’s precedent nor is compelled by our decisions. As the Commission failed adequately to explain the adoption of the new test, we remand the orders for reconsideration. 2
I
Great Lakes operates an interstate pipeline that runs some 2,000 miles from the Canadian border in Wisconsin to the Canadian border in eastern Michigan. TransCana-da is an affiliate of Great Lakes and uses about 80% of the pipeline’s capacity. The present case arises from two rate filings under Section 4 of the Natural Gas Act, 15 U.S.C. § 717c (1988), in which Great Lakes sought to recover the cost of several expansion projects designed to increase the pipeline’s capacity.
Opinion 367
The filing at issue in
Opinion 367
covered expansion projects built to service petitioners TransCanada and Northern Minnesota Utilities. The projects cost some $557 million, which more than doubled Great Lakes’ preexisting rate base from $393 million to $950 million. Great Lakes filed a rate increase request that proposed rates to be calculated by rolling in the expansion costs. The Commission set all the issues for an evidentiary hearing except the question of whether rolled-in rates should be allowed; on that question the Commission ordered “paper hearing” procedures. See
Great Lakes Gas Transmission L.P.,
After considering the submissions the Commission held that Great Lakes must “specifically address and justify rolled-in rates by showing that systemwide benefits to existing customers are commensurate with the increase in rates.”
See Opinion 367,
57
*308
Opinion 368
In this proceeding the Commission considered Great Lakes’ request to recover rolled-in rates for two expansion projects built to serve petitioners TransCanada and Midland Cogeneration Venture, with a total cost of $190 million. The rate filing was heard by an Administrative Law Judge (“ALJ”) with the participation of Commission staff. The ALJ ruled that rolled-in rates were permissible under Commission precedent.
See Great Lakes Gas Transmission L.P.,
II
A
Petitioners contend that the standard by which the Commission judged Great Lakes’ rate filing represents an unexplained departure from Commission precedent, and thus constitutes arbitrary decisionmaking under the Administrative Procedure Act.
See 5
U.S.C. § 706(2)(A) (1988);
Michigan Consol. Gas Co. v. FERC,
The Commission concedes that it weighed costs and benefits, but maintains that it has always done so. The only distinctive feature of the Great Lakes orders was that the Commission subjected the claimed benefits to a more rigorous scrutiny because the magnitude of the projects threatened a massive shift of costs onto existing customers. All concerned thus agree on the nature of the test the Commission applied in the present orders; the dispute stems rather from opposed descriptions of the Commission’s precedent.
Petitioners have the better of the argument. At least since
Battle Creek Gas Co. v. FPC,
Until quite recently the approach detailed in
Battle Creek
has prevailed without serious challenge. A particularly clean example of the Commission’s normal practice appears in
Great Lakes Gas Transmission Co.,
The Commission reverses the ALJ’s decision and concludes that the rates ... should be computed on a rolled-in basis. It is true that the facilities were built for [a particular customer’s benefit]_ How *309 ever, the question is whether the T-6 and T-9 facilities have been shown oh this record to be beneficial to other customers of Great Lakes_ The Commission believes that all mainline facilities benefit all customers even though certain facilities may have been added at some time to increase mainline capacity in order to serve a particular customer.... The Commission cautions that it is not necessary to have measurable benefits to justify rolling-in costs. It is sufficient that the quality of the system’s services is enhanced by the presence of the facilities in question.
Id. at 61,700-01 & n. 55.
The Commission points to a pair of cases decided four months before the Great Lakes orders presently under review. In
Colorado Interstate Gas Co.,
The Commission also argues that, whatever its previous policies, our decision in
Algonquin Gas Transmission Co. v. FERC,
Algonquin undoubtedly does require a reasonably specific qualitative description of the systemwide benefits of an integrated facility. But the Court was careful not to require a balancing of costs and benefits (much less a quantification thereof), and indeed confirmed that the general test for rolling-in was the same that Great Lakes discerns in Commission precedent:
In Great Lakes Gas Transmission Co.,45 FERC ¶61,237 at 61,701 n..55 (Nov. 17, 1988), the Commission stated that a roll-in is warranted when “the quality of the system’s services is enhanced by the presence of the facilities in question.” We do not quarrel with that standard.... What we do require, however, is that the Commission, before ordering a roll-in under Section 5(a), offer more than a conclusionary statement that the existence of system-wide benefits renders it unjust to allocate facilities costs incrementally.
Algonquin,
B
The novelty of the Commission’s test required a reasoned explanation for the change. Our ability to discern such an explanation is hampered by the Commission’s claim on appeal that no change in course took place. Nonetheless both orders obliquely recognized and sought to justify the new test. The Commission stated in Opinion S67 that:
The basic test has always involved a weighing of costs and benefits. However, in the past, the Commission took a broader view regarding the value of system expansions to existing customers than we have in recent cases. This is, in part, because the *310 increased costs to existing customers resulting from rolled-in pricing were generally relatively small compared to the obvious systemwide benefits in the form of increased capacity, reliability, and flexibility. However, more recently, the Commission’s focus on the value of the benefits of expansions to systemwide customers has intensified as costs have risen considerably in relation to the benefits.
In these passages the Commission “eross[ed] the line from the tolerably terse to the intolerably mute.”
Greater Boston Television Corp. v. FCC,
The Commission’s assertion that the costs of expansion have recently increased in relation to benefits failed to address record evidence to the contrary. Great Lakes attempted to show that, in constant 1990 dollars, the average investment cost of the expansion facilities (calculated per Mcf/mile) was some 15% lower than the average historical investment cost of the pre-expansion components of the Great Lakes system. See Exh. GL^4, System Investment Cost per MMcf-Mile, Joint Appendix [“J.A.”] 3392-93. The Commission failed to make clear why the gross cost of an expansion bears on the proper choice of rate structure if that cost does not have a proportionate effect on the rates charged to pre-expansion customers. Great Lakes maintains that high cost need not produce higher rates, because large expansions increase the pipeline’s capacity and thus increase the pipeline’s revenue as well.
The Commission, of course, has no obligation to apply that theory, but given the record support offered by Great Lakes it should at least respond to it. The Commission made but a cursory effort to calculate the rate increase to pre-expansion customers that a roll-in of the expansion costs would produce. In
Opinion 368,
for example, the Commission asserted that “the rate increase as a result of these expansions totalled $33.3 million.”
The Commission seems to have adopted a similar distinction between total cost and rate effects in
Northwest Pipeline Corp.,
The Commission’s explication of the commensurate benefits test displays- a further deficiency. The Natural Gas Act prohibits rates that are “unduly discriminatory” or “preferential.” 15 U.S.C. §§ 717c(b), 717d(a). Of course rate differences founded on relevant differences of fact do not constitute rate discrimination.
See TransCanada
*311
PipeLines Ltd. v. FERC,
We do not reach that ultimate question of statutory construction, for the Commission faltered in its antecedent duty to explain how incremental pricing relates to the prohibition against discriminatory rates. The orders were content to state that
these price differentials [caused by incremental rates] merely reflect the costs to expand the pipeline’s capacity at a different time and for different customers.... [T]he cost of providing service to [petitioners] required major capacity additions at a much greater cost than the cost of providing service to existing shippers.
Opinion 367,
First, petitioners insist that expansions are caused by the requirements of the existing customers as well as the expansion customers; all customers create the need for the total system capacity. The Commission acknowledged that Great Lakes is a “fully integrated system, both physically and operationally.”
Opinion 367,
Second, the Commission should consider the consequences of incremental pricing for future customers who subscribe to expansion services that were incrementally priced when first built. Commission counsel indicated at oral argument that the cost of providing service to such customers would be rolled in to the portion of the rate base attributable to the expansion facilities, resulting in a multi-tiered system under which the various classes of customers would each pay a separate rate. Of course that representation cannot bind the Commission itself,
cf. SEC v. Chenery Corp.,
Ill
The orders are remanded for further proceedings consistent with this opinion.
It is so ordered.
Notes
. Under incremental pricing the costs of particular facilities are assigned to particular customers and recaptured by increasing the rates charged to those customers. Under rolled-in pricing the costs of the facilities are added to the pipeline's total rate base and recaptured by an increase in the general rate charged to all customers in proportion to the pipeline capacity they use.
. Our disposition of the case makes it unnecessary to consider the independent claim, advanced by petitioner Northern Minnesota Utilities ("NMU”), that the costs particularly attributed to NMU's expanded service should have been rolled in even if the costs attributed to other petitioners were incrementally priced.
