Opinion for the Court filed by Circuit Judge GINSBURG.*
Dissenting opinion filed by Senior Circuit Judge BAZELON.
GINSBURG, Circuit Judge:The authority of the Federal Energy Regulatory Commission (FERC or Commission 1) to license the construction of a hydroelectric plant on a body of water subject to federal jurisdiction is limited by two federal statutes: the Federal Power Act (FPA), 16 U.S.C. §§ 791a-823a (1976 & Supp. V 1981), and the National Environmental Policy Act (NEPA), 42 U.S.C. §§ 4321-4361 (1976). In this petition for review, Friends of the River and Dale Meyer (FOR or petitioners) challenge as inconsonant with both statutes FERC’s license to the Calaveras County Water District (CCWD) to operate a hydroelectric plant on the North Fork Stanislaus River in California. We find that in one respect FERC did not attend with due care to NEPA’s procedural requirements. Because we conclude that the Commission’s decision is in other respects unassailable, and because a remand to cure the procedural lapse would serve no sensible purpose, we affirm the Commission’s action.
I. Background
In November 1978, CCWD, a California county water district, applied to FERC for a license to construct a hydroelectric plant (the project or the Calaveras project) on the North Fork Stanislaus River in Alpine, Tuo*332lumne, and Calaveras Counties, California.2 The project, as described in CCWD’s application, involves the construction of a series of dams, the enlargement of an existing reservoir, and the construction of two new powerhouses. As planned, the project will produce an average annual energy yield of over 500 gigawatt-hours (Gwh), equivalent to the energy produced by roughly one million barrels of oil, and have a total power capacity of about 200 megawatts (MW).3
The principal ecological effect of the plant will stem from the enlargement of the Spicer River Reservoir, which at its maximum elevation will inundate approximately 1,780 acres of forest, meadow, and riparian habitat. While the reservoir will be moderate in size compared to nearby water projects, the loss of Gabbot Meadow, part of the inundated area, is likely to have a negative effect on deer and other wildlife populations. In its total dimension, the project will mean the loss of about 2,500 acres of wildlife habitat.
The power generated by the project is to be sold to the Northern California Power Agency (NCPA).4 NCPA is a consortium of twelve small utilities, each responsible for the retail distribution of electrical power within its service area. At the time of the 1978 application, the NCPA utilities did not generate any of the power they supplied to their customers; instead, they relied entirely on power purchased from Pacific Gas and Electric Company (PG & E), the largest electrical utility in California, and from the Central Valley Project (CVP), also located in California, of the federal Western Area *333Power Administration. NCPA, and a number of other utilities, including CVP, are bundled together with PG & E to compose a “PG & E area” for purposes of statewide planning by the California Energy Commission (CEC). Electricity Tomorrow 49. NCPA’s relationship with PG & E, however, is purely contractual. PG & E’s charter does not place it under a legal obligation to supply power to NCPA or to customers within NCPA’s service area. Rather, PG & E’s priority charge is to supply customers within its own service area as defined by its charter, an area distinct from NCPA’s.
NCPA intervened in the licensing proceedings before FERC immediately after CCWD filed the 1978 application. For NCPA, the project represents an important step towards energy self-sufficiency in the years to come. For CCWD, the project means an increase in the firm yield of water on the North Fork Stanislaus River; in addition, revenue generated by the project can be applied to the cost of the water CCWD provides, and can be used, in the future, to finance additional water projects in the district.
Litigation aimed at stopping the project began soon after CCWD filed the 1978 license application, when FOR filed suit in state court claiming that the environmental impact report filed by CCWD pursuant to the California Environmental Quality Act did not satisfy the requirements of that Act. In 1979, judgment was entered in California Superior Court rejecting all claims made by environmental plaintiffs.5
FERC commenced its investigation of the desirability of the Calaveras project in 1978. In late 1979, it issued a draft environmental impact statement (EIS) setting forth the environmental impacts of the project. It received extensive comments on the draft EIS from federal and state agencies as well as private parties, and issued a revised, final EIS in 1980. That document accorded only summary attention to the concern— raised before the agency — whether, in lieu of the project, NCPA’s power needs could be met by continued reliance on purchases from other utilities. The Commission did state in the EIS that power purchase contracts between NCPA members and PG & E “can be terminated on 6 to 24 months notice and cannot be considered as firm resources,” J.A. 187; it further stated that resort to other sources of energy, including purchased power, in preference to licensing the hydroelectric Calaveras project, “would consume nonrenewable fossil-fuel resources.” J.A. 328. FERC took testimony commenting on the final EIS at public hearings in Washington, D.C. and Angels Camp, California.
In February 1982, FERC issued an order and opinion granting CCWD a license to construct the Calaveras plant. It denied FOR’s petition for rehearing in an opinion issued in July 1982. The July order explained more cogently why the Commission rejected prospects for further reliance on purchased power as a ground for refusing the license. FERC observed that “PG & E’s [own] ability to meet load in the future is uncertain,” J.A. 960, and cited studies, in Electricity Tomorrow and a later (March 1981) CEC staff report, supporting that conclusion.
Petitioning for our review of the Commission’s grant of the license, FOR contends that the Commission has neglected its duties both under the FPA and under NEPA; we consider separately below FOR’s challenges under each statute.
II.' FPA Claims
Section 10(a) of the Federal Power Act provides that the Commission may issue *334a license for a hydroelectric plant only where
the project ... shall be such as in the judgment of the Commission will be best adapted to a comprehensive plan for improving or developing a waterway or waterways for the use or benefit of interstate or foreign commerce, for the improvement and utilization of waterpower development, and for other beneficial public uses, including recreational purposes.
Federal Power Act, 10(a), 16 U.S.C. § 803(a) (1976). Pursuant to this provision, the Commission has a multifaceted obligation to investigate, before approving any license, whether construction of the project is in the public interest. Udall v. FPC, 387 U.S. 428, 87 S.Ct. 1712, 18 L.Ed.2d 869 (1967). Once the Commission makes its investigation, however, its findings may be upset on judicial review only if they are not supported by substantial evidence. 16 U.S.C. § 8251 (b) (1976); see Scenic Hudson Preservation Conference v. FPC, 453 F.2d 463, 467-68 (2d Cir.1971) (Udall did not overturn the traditional “substantial evidence” review standard), cert. denied, 407 U.S. 926, 92 S.Ct. 2453, 32 L.Ed.2d 813 (1972).
FOR asserts the inadequacy of FERC’s decisionmaking in multiple respects. Petitioners claim that need for the project has not been demonstrated; FERC, they contend, has overprojected demand for power in NCPA’s service area, and underprojected supply. Moreover, petitioners charge that FERC improperly rejected reasonable alternatives, including purchase of power from other utilities, and alternate means of constructing the project. FOR further argues that FERC misconceived the overall negative environmental effects of the project, and misjudged what is in California’s “public interest,” by overlooking state policy that attaches a low priority to new hydroelectric projects.
Our review securely indicates that only one of FOR’s claims warrants discussion — the claim that the project is unnecessary because NCPA can continue to purchase all the power it needs. FOR’s other contentions are insubstantial. The administrative record fully supports FERC’s appraisal of projected NCPA demand for power,6 and the Commission’s evaluation of future NCPA generating capacity.7 Substan*335tial evidence in the record also supports FERC’s rejection of the Utica-Union, Low Spicer Storage Complex alternative to building the CCWD project at its present location. Equally adequate evidence backs up FERC’s conclusion that the environmental impact mitigation measures negotiated by CCWD, the California Department of Fish and Game, and the U.S. Forest Service are reasonable and attainable. California’s announced policy concededly ranks large hydroelectric projects low among possible new power plant development, but ample evidence sustains FERC’s independent determination, as a federal agency, that the licensed hydroelectric plant is an appropriate development.8
FOR urges most strenuously that FERC should have declared the project unnecessary because NCPA’s power needs can be met reliably through continued purchases from PG & E, NCPA’s traditional source of electric power. FERC responded that
PG & E’s ability to meet load in the future is uncertain. Under adverse hydrological conditions, PG & E’s reserve margin in 1985 could be as little as 3 percent. Moreover, ... by 1992 the PG & E system will require, in addition to the [Calaveras] and another proposed hydroelectric project, an additional 493 MW of new capacity to be able to provide reliable electric service.
Order Denying Rehearing, J.A. 959, 960. FERC has also noted that the NCPA-PG & E purchase contracts are terminable by PG & E on six to twenty-four months notice, and that PG & E’s priority responsibility is to customers within its own service area. J.A. 187, 411, 443. These findings, FERC argues, more than adequately justify its conclusion that NCPA cannot safely rely on PG & E power, and should be permitted to develop the capacity to stand on its own feet in the years to come.
We examine in turn FOR’s assertions that (1) substantial evidence does not underpin FERC’s conclusion that PG & E’s own resources will be insufficient to support NCPA’s growing needs, and (2) even if PG & E’s resources, considered in isolation, are inadequate to support NCPA, FERC should have extended its examination to the energy resources of utilities beyond PG & E, resources that could be made available to PG & E “during emergency conditions.” Brief for Environmental Petitioners at 20.
A. Extent of PG & E’s Own Resources
The most up-to-date set of energy forecasts in the agency record indicates that peak demand9 in the PG & E planning area will rise to 19,407 MW by 1992. Electricity Tomorrow 62. To meet a peak demand increase of this magnitude, PG & E will have to add 4,376 MW of capacity over and above what it now has. Id. Further, PG & E’s current reserve margin is “well below the optimum,” Id. at 22; to bring its reserve margin up to a safe level, PG & E will have to add an additional 1,394 MW by 1992. Id. at 67. Finally, PG & E cannot securely rely on all the power it is receiving now; some of its generating plant is outmoded, and all of its long-term contracts for purchase of firm capacity from other utilities are due to expire in the 1980s. Even assuming renewal of two long-term contracts with Pacific Northwest utilities, PG & E will have to *336add 1,754 MW of capacity to make up for retirements and contract expirations. Id. at 67-68. In sum, based on forecasts in the record, PG & E, to stay safe, must add a minimum of 7,524 MW of capacity by 1992 —a figure equivalent to about half of PG & E’s current demand.
To meet its energy needs, PG & E has developed a comprehensive plan to build coal-fired, hydroelectric, and cogeneration plants. The plan is dominated by additions of nuclear power plants in the early 1980s and coal-fired capacity in later years. Electricity Tomorrow 328. It appears that PG & E — and CEC — have included the Calaveras project in their resource planning.10
Even including the Calaveras project in the estimation, however, PG & E faces a shortfall in capacity additions reasonably expected to be operating by 1992.11 Just how PG & E is to make up this shortfall is not clear. One CEC staff report asserts that additional efforts along lines such as conservation and further geothermal generation will be sufficient. J.A. 987-92. The extent of PG & E’s future capacity needs, however, together with the utility’s heavy reliance on nuclear power generation, may place PG & E in an uncomfortable position in the next few years. Electricity Tomorrow reports that “if Diablo Canyon [nuclear power plant] is not licensed and operated, the PG & E area may require assistance from other utilities if unscheduled very large power plant outages are experienced.” Electricity Tomorrow 316. CEC studies further indicate that in a worst-case analysis, viewing the PG & E planning area as an isolated system, PG & E’s reserve margin could drop as low as 2.7% by 1985, more than 10% below optimum levels. Id. at 317. While other utilities could come to PG & E’s rescue in emergency conditions, the prospect remains that PG & E will end up in the next few years not as a seller of surplus energy but, to meet its own needs, as a purchaser of power from other systems with surplus supplies. See Electricity Today 331 (“The potential delay in obtaining the Diablo Canyon operating licenses has prompted PG & E to seek purchases of short-term capacity.... ”). This state of affairs has persisted. See Power Shortage — Or Sham?, Newsweek, June 13, 1983, at 64 (“PG & E remains confident it can help fill its growing needs by purchasing power from other systems with surplus supplies.”).
CEC’s apparent inclusion of the Calaveras project in its resource planning indicates the vulnerability of POR’s assertions concerning the adequacy of PG & E’s resources. FOR maintains that NCPA can rely on power from PG & E. FOR cites in support of its assertions, however, CEC studies that assume PG & E’s reliance on power from NCPA. CEC has found, moreover, that even if Calaveras is built, PG & E, if it is to bolster its reserve margin, will still need extensive capacity additions. FOR can thus tenably argue only that, if the Calaveras project is not built, some other project somewhere else perhaps could be built to take up the slack. But this possibility hardly undercuts the substantial record support for FERC’s finding that PG & E’s resources do not obviate the need for power the Calaveras project will generate.
B. Purchases from Beyond PG & E
FOR next argues that even if the Commission acceptably analyzed PG & E’s own *337resources, FERC did not go far enough. The Commission should have looked beyond California, FOR maintains; it should have extended its supply-demand analysis to the Pacific Northwest. FERC indicated that it regarded interconnections with utilities outside California as a speculative matter; it said in response to comments on the draft EIS:
An additional intertie with the Pacific Northwest would not provide the dependable capacity equivalent to the proposed project. The amount of power available from the Pacific Northwest depends on the magnitude of the power loads in the Pacific Northwest and the amount of water available for generation. At times, there is no power available for transfer from the Pacific Northwest, and, as future loads in that area increase, less power will be available to California.
J.A. 415. Concededly, FERC did not undertake detailed examination of resources beyond PG & E’s. It did not attempt to estimate what PG & E might buy from Oregon, Washington, British Columbia, and Manitoba, and sell to NCPA. We conclude that FERC was not required to enlarge its inquiry as FOR proposed.
Regional power planning is difficult and uncertain; it becomes increasingly difficult and uncertain as its scope is extended in time and space.12 One scholar has characterized regional power planning as “a task that confronts a degree of uncertainty and risk without historical precedent.”13 As to the Pacific Northwest, the same author stated: “[T]he best one can do” in that region with current planning methods still entails “major risks” of faulty prediction.14
FERC initially analyzed projected supply and demand in NCPA’s service area and found a need for new generating capacity. FOR pointed to the supply source next door, PG & E. FERC examined PG & E’s projected reserve margin and found it low; PG & E, it is reasonably anticipated, will need new sources of power even on the assumption that CCWD’s project is built. FOR contends FERC should have proceeded to the next door, a very large one, the Pacific Northwest.15 FERC’s terse response is not surprising. No one, apparently, has made projections that would justify *338safe reliance on Northwest power. California itself subdivides the state into distinct “planning areas”; CEC has noted that one of the state’s objectives is to meet demand while “not substantially increasing power purchases from utilities outside California.” Electricity Tomorrow 354.16
We are in no position to require FERC, in the circumstances of this case, to survey power availability more broadly than it did. How far in time and space a power projection investigation ought to extend is a question involving practical considerations of feasibility and a balancing of costs against expected useful results. Resolving these issues requires technical expertise and is properly left to the informed discretion of the responsible federal agency. Cf. Kleppe v. Sierra Club, 427 U.S. 390, 412, 96 S.Ct. 2718, 2731, 49 L.Ed.2d 576 (1976). It is impossible to say, on review of the record before us, that FERC failed to exercise its discretion intelligently.
Udall v. FPC, 387 U.S. 428, 87 S.Ct. 1712, 18 L.Ed.2d 869 (1967), a lead decision in this area, does not counsel a different result. It involved a controversy between the Secretary of the Interior and the FPC. Interior initially took the position that a consortium of four private utilities should not be licensed to develop a hydroelectric project on the Snake River at the Idaho-Oregon border until means of protecting anadromous fish (principally salmon and steelhead) had been studied. Later, Interior added its view that the project should be constructed by the federal government, not by private utilities; further, Interior questioned the immediate need for the plant. The FPC nevertheless approved the utilities’ proposal. The Court, per Justice Douglas, overturned that decision, and remanded the matter to the FPC.
The Court identified as the primary ground for remand the agency’s failure to take evidence on whether development of the river basin should proceed under federal rather than private, state, or municipal auspices. Id. at 431-32, 87 S.Ct. at 1714. It observed that the issue of federal, as distinguished from private or municipal, control “[might] conceivably make a vast difference in the functioning of the vast river complex” in question. Id. at 435, 87 S.Ct. at 1716. “Since the cases [had to] be remanded to the Commission,” the Court thought it appropriate to instruct the agency to consider as well the alternative of no development at all. Id. at 436, 87 S.Ct. at 1716.
In the wide-ranging discussion in the second part of the Udall v. FPC opinion, the Court conveyed this message: where a project may have major adverse environmental effects, the Commission should carefully consider the need for the project, in light of its multiple impacts on commerce, recreation, wilderness and wildlife preservation, before granting a license. A determination of need, the Court said,, required more than affirmation that the project would be “beneficial to the licensee” combined with ascertainment that the region would “be able to use the additional power.” Id. at 450, 87 S.Ct. at 1724.
The project proposed in Udall v. FPC risked “destroying] the river as a waterway,” yet the agency had not addressed “the desirability of [the river's] demise.” Id. The Court declared that the Commission should have explored alternate sources of power supplies, and the regional and even national need for the recreational and commercial resources, including fish and other wildlife, threatened by the project in question. Id. at 440, 442, 444, 450, 87 S.Ct. at 1718, 1719, 1720, 1724.17 The public in*339terest determination under section 10(a) of the Federal Power Act,18 in sum, should be overarching, the Court said; it should encompass the effects of the proposed project on navigation, water supply, recreation, and other public uses of a waterway, and not simply regional power demand.
In the case at hand, FERC’s performance is hardly comparable to the FPC’s in Udall v. FPC. The Commission did not restrict its inquiry to the benefits of the project to CCWD and NCPA. Nor did it stop at the region’s demand for additional power. It took into account alternate sources of power within the region, and the interest in preserving the region’s wilderness areas and wildlife. It cannot fairly be faulted, as the Court indicated the agency could in Udall v. FPC, for wholesale neglect of issues relevant to the public interest.
One portion of Justice Douglas’ opinion in Udall v. FPC, it is true, broadly discusses the entire world’s future supplies of power, and suggests that hydroelectric projects should be evaluated'in light of the fact that “My the end of the century ‘nuclear energy may account for about one-third of our total energy consumption.’ ” Id. at 446-47, 87 S.Ct. at 1721-23 (quoting Brown, The Next Hundred Years 109 (1957)). But this part of the decision does not instruct the Commission on how far afield it should go in considering alternate power sources. The opinion quotes a long passage from Interior’s petition to intervene in the FPC proceedings, in which Interior included a list of Northwest power resources inside and outside the utilities’ service areas. 387 U.S. at 444-46, 87 S.Ct. at 1720-21. As far as one can tell from the opinion, however, the only alternate sources of power the Court noted as immediately relevant to the FPC’s decision were projects physically located within the service area of the utilities the FPC had licensed. Id. at 448, 87 S.Ct. at 1723. All one can conclude from this less than crystalline part of Udall v. FPC is that the Commission must look beyond any single utility’s or consortium of utilities’ independent resources. FERC did that in this case.
We hold that the Commission did not abuse its discretion in declining to pursue an investigation into the amount of power PG & E might be able to purchase from Pacific Northwest utilities. FERC’s decision to limit close consideration of demand and resources to meet the demand to the NCPA and PG & E areas, and to avoid an excursion into more distant regions, was reasonable and comfortably within the Commission’s authority.19
III. NEPA Claims
FOR reasserts under a NEPA heading several of the contentions we found *340insubstantial when raised under an FPC rubric. See supra pp. 97-99. We find them no more worthy of discussion when presented under a different label.20 We can deal summarily as well with FOR’s contention that the EIS should have examined “water supply” aspects. CCWD’s plans in this regard were not sufficiently concrete to warrant evaluation in conjunction with the Calaveras power project. See Kleppe v. Sierra Club, 427 U.S. 390, 401-02, 96 S.Ct. 2718, 2726, 49 L.Ed.2d 576 (1976).21
FOR’s claim concerning the prospect of purchasing power in lieu of constructing a hydroelectric plant, however, bears separate discussion in the NEPA context. To the extent that FOR challenges the size of the region considered by FERC — the dimensions of the Commission’s investigation— our discussion relating to the FPA largely answers FOR’s criticism and we need not write many more words here. FOR raises a graver concern with respect to the timing of the investigation the Commission did undertake; FOR’s final contention concerning the need for a supplemental EIS on the other hand, does not require extended discussion.
A. The Dimensions of FERC’s Investigation
Section 102(2)(E) of NEPA calls upon each federal agency to “study, develop, and describe appropriate alternatives to recommended courses of action in any proposal which involves unresolved conflicts concerning alternative uses of available resources.” 42 U.S.C. § 4332(2)(E) (1976). This provision parallels the general EIS requirement of discussion of “alternatives to the proposed action.” Id. § 4332(2)(iii). FOR contended that the Commission was obliged to look to PG & E and beyond to satisfy the command in Udall v. FPC, supra, that the agency, in carrying out its mission under the FPA, explore “alternative sources of power.” We have explained above why the examination FERC conducted satisfied the FPA requirement and was consistent with the Court’s instructions in Udall. See supra pp. 100-103. FOR makes the same arguments in contending that purchasing power was an “alternative” the Commission should have considered expansively to carry out its obligations under NEPA.22
We note initially that it is not altogether apparent why power purchasing should rank as a course “alternative” to power generation. Purchasing prospects are perhaps more appropriately considered a component of need. Power purchasing is feasible and desirable only if a producer in the relevant region has excess supplies to sell, supplies adequate to obviate the need for new production in the area. FOR’s dominant claim is not that FERC failed to con*341sider “alternative” courses for production of power, but that there was no need for additional power generation.23 However, this court has once before accepted categorization of purchased power as an “alternative” within the meaning of NEPA,24 and we will adhere to that view.
Just as we ruled in considering FPA strictures that FERC was not obliged to survey power availability more broadly than it did, so we conclude here that the Commission properly confined its consideration of demand and available power supplies to the NCPA and PG & E areas. And for the same reasons. We add only the Supreme Court’s admonition in Vermont Yankee Nuclear Power Corp. v. NRDC, 435 U.S. 519, 98 S.Ct. 1197, 55 L.Ed.2d 460 (1978), that “the concept of alternatives [under NEPA] must be bounded by some notion of feasibility.” Id. at 551, 98 S.Ct. at 1215.25 FERC’s decision as to the space dimensions of its demand and supply exploration in this case was properly bounded by reasonable considerations of what could be forecast with a fair degree of reliability and with the energy, research, and time resources available to the agency. See NRDC v. Morton, 458 F.2d 827, 837 (D.C.Cir.1972).26
B. The Timing of FERC’s Investigation
We are secure in the conclusion that the Commission’s investigation of power purchasing as a means to satisfy NCPA’s need, or as an “alternative” course, was substantively unassailable. However, an important question remains whether the license should be set aside and the matter returned to FERC because the agency did not present its analysis adequately in the EIS itself; instead, the Commission delayed adequate statement until its July 1982 order denying FOR’s rehearing petition.
The crux of the problem here lies in the difference between typical “substantial evidence” review of agency decisionmaking on the one hand, and NEPA review on the other. “Substantial evidence” review essentially concerns the merits of the decision ultimately reached by the agency — is that decision sustained by the evidence in the record taken as a whole? See Universal Camera Corp. v. NLRB, 340 U.S. 474, 71 S.Ct. 456, 95 L.Ed. 456 (1951); American Public Gas Association v. FPC, 567 F.2d 1016, 1028-29 (D.C.Cir.1977), cert. denied, 435 U.S. 907, 98 S.Ct. 1456, 55 L.Ed.2d 499 (1978). Substantial evidence there must be, but that evidence may be scattered throughout the record. NEPA, on the other hand, establishes an • “essentially procedural” requirement. Vermont Yankee Nuclear Power Corp. v. NRDC, 435 U.S. 519, 558, 98 S.Ct. 1197, 1219, 55 L.Ed.2d 460 (1978). It calls upon agencies to present *342evidence and discussion relevant to their environmental decisionmaking in one comprehensive document — the environmental impact statement.
Section 102(2) of the Act
requires that responsible officials of all agencies prepare a “detailed statement” covering the impact of particular actions on the environment, the environmental costs which might be avoided, and alternative measures which might alter the cost-benefit equation. The apparent purpose of the “detailed statement” is to aid in the agencies’ own decision making process and to advise other interested agencies and the public of the environmental consequences of planned federal action.... Moreover, by compelling a formal “detailed statement” ..., NEPA provides evidence that the mandated decision making process has in fact taken place and, most importantly, allows those removed from the initial process to evaluate and balance the factors on their own.
Calvert Cliffs' Coordinating Committee v. AEC, 449 F.2d 1109, 1114 (D.C.Cir.1971). The EIS serves as an assurance that the agency has indeed adverted closely and carefully to the environmental impacts of its actions. By “gathering] in one place a discussion of the relative environmental impact of alternatives,” NRDC v. Morton, 458 F.2d 827, 834 (D.C.Cir.1972), the EIS makes it possible for the public and reviewing courts to consider conveniently how and why the agency made its final choices. See generally Grazing Fields Farm v. Goldschmidt, 626 F.2d 1068 (1st Cir.1980). And of particular importance, the EIS requirement inhibits post hoc rationalizations of inadequate environmental decisionmaking.
FERC, we are impelled to say, did not measure up to NEPA’s command. Most of FERC’s analysis of the power purchase issue appears in the Commission’s July 1982 order, not in the EIS. Were we confronted with the slim references to the question in the EIS itself, unsupplemented by the discussion in the July 1982 order, we might consider a remand unavoidable. Once power purchasing is ranked an “alternative” course for NEPA purposes, see supra p. 104, a reviewing court appears bound to. conclude that what FERC reported in the EIS was inadequate.
The special circumstances this case presents, however, deter us from ordering a remand so that FERC can compose a new EIS. This court has recognized that “[t]he EIS ... is not an end in itself, but rather a means toward the goal of better decision-making.” North Slope Borough v. Andrus, 642 F.2d 589, 599-600 (D.C.Cir.1980). A remand here, we believe, would treat the EIS as “an end in itself” and would not meaningfully serve NEPA’s goals.
Were we to return the case, the Commission would be instructed to evaluate prospects for NCPA’s continued reliance on purchasing power rather than generating it, and to write up the evaluation in the form of an EIS. But well before the start of this review proceeding, the Commission did make such an investigation, after receiving and responding to extensive comments from interested persons outside the agency, and FERC incorporated its findings in an opinion accessible to the public — the July 1982 order. Thus a remand here is not needed to “aid in the agencies’ own [environmental] decision making process,” Calvert Cliffs' Coordinating Committee v. AEC, 449 F.2d at 1114, for that process has already occurred and we have set out our reasons for finding it bona fide and sufficiently extensive. See supra pp. 99-103. The Commission’s July 1982 order, read in conjunction with the EIS, adequately “advise[s] other interested agencies and the public” of FERC’s reasoning and the information on which it rests. Id.27 We are not left to rely on post hoc rationalizations, see Motor Vehicle Manufacturers Association v. *343State Farm Mutual Automobile Insurance Co., - U.S. -, 103 S.Ct. 2856, 2870, 77 L.Ed.2d 443 (1983); we have before us FERC’s assessment, embodied in an opinion composed after due investigation and before the matter was brought to court.28 Sending the matter back “to teach the agency a lesson” would be an essentially punitive measure; we can discern no benefit to the public in such a course, and no genuine service to the policies NEPA advances.
The result we reach, and the reasons for it, are not novel. We note particularly Scenic Hudson Preservation Conference v. FPC, 453 F.2d 463 (2d Cir.1971), cert. denied, 407 U.S. 926, 92 S.Ct. 2453, 32 L.Ed.2d 813 (1972), involving a hydroelectric plant, licensed by the Commission, with no document on file titled an EIS. The Commission had rendered a comprehensive opinion, however, which included considerable discussion of environmental impacts. Though NEPA governed, the court saw no purpose in a remand so that the agency’s discussion could be circulated for comment under a corrected label. It sufficed that the Commission’s opinion demonstrated “full compliance with the National Environment Policy.” Id. at 48129
A more conspicuous default is described in Warm Springs Dam Task Force v. Gribble, 621 F.2d 1017 (9th Cir.1980). There, new information about earthquake fault lines matured the Army Corps of Engineers’ obligation to supplement an EIS it had filed prior to beginning construction of a dam in Sonoma County, California. The district court, ruling on a suit filed by environmentalist groups to enjoin further construction, found that the Corps had complied with NEPA even though it had taken no action to investigate the earthquake safety problem. The Ninth Circuit disagreed — the Corps had unlawfully ignored its obligation to investigate. The appellate court noted, however, that subsequent to the start of the district court hearing the Corps had finally ordered studies; and those studies largely obviated seismic safety concerns. It therefore declined to remand; it would be pointless, the Ninth Circuit said, to “order the Corps to conduct studies already completed to answer questions the Corps has already answered on a basis that could not be successfully challenged.” Id. at 1026.30
Finally, in Swinomish Tribal Community v. FERC, 627 F.2d 499 (D.C.Cir.1980), our court confronted a situation similar to the one at hand. The Commission’s EIS, covering construction of a hydroelectric plant, failed to discuss at all the alternative of building a dam lower than the one proposed. There was nothing facially unreasonable about building the lower dam. The Commission eventually discussed the lower dam alternative at reasonable length; as in this case, much of the discussion appeared in the Commission’s order denying rehearing. We quoted from FERC’s order denying rehearing, concluded that the Commission had given the lower dam alternative *344the requisite consideration, id. at 514, and affirmed the Commission’s action.31
We appreciate the need for caution in cases in which an agency slights the EIS requirement. A reviewing court must be certain that the basic policies of NEPA are satisfied, and that a remand would indeed be pointless, before it rejects that course. Arizona Public Service Co. v. FPC, 483 F.2d 1275 (D.C.Cir.1973), is illustrative. That case involved the Commission’s denial of a license to transport natural gas, an action that arguably had a significant effect on the environment. But no EIS was filed, nor did any agency statement account for the omission. The court was not positioned to say whether the agency in fact engaged in sound environmental decisionmaking, for nothing in the record demonstrated that it had. Remand is essential in such a case.
We recognize too that language can be found in decisions suggesting that pleas of “futility” will never do to justify noncompliance with NEPA. Invariably, such statements appear when there is no cogent demonstration, of the kind made here, that the agency gave due consideration to the relevant environmental factors and made that consideration manifest in an accessible,32 intelligible33 form. Understandably, courts have low tolerance for futility arguments pressed by parties who seek release from, an obligation to engage in serious environmental decisionmaking on the ground such an enterprise would not change the party’s mind about a planned development. See, e.g., Jones v. Lynn, 477 F.2d 885 (1st Cir.1973); Hanly v. Mitchell, 460 F.2d 640, 648 (2d Cir.), cert. denied, 409 U.S. 990, 93 S.Ct. 313, 34 L.Ed.2d 256 (1972); Pennsylvania v. Morton, 381 F.Supp. 293, 300 n. 14 (D.D.C.1974); City of New York v. United States, 337 F.Supp. 150 (E.D.N.Y.1972).
But insistence on form when we have before us a case in which the agency did in fact “compl[y] with the National Environment Policy,” Scenic Hudson Preservation Conference v. FPC, 453 F.2d at 481, would jeopardize NEPA’s “lofty declarations.”34 Remands in such cases would inevitably breed cynicism about court commands; they would likely yield going-through-the-motions responses on the part of those told to attend to the court’s costly, resource-consuming instruction to redo, under the proper heading, what has already been done effectively.
C. Supplementation of the EIS
FOR urges, referring to submissions annexed to its brief, and its Application for Leave to Adduce Additional Evidence before FERC and Motion for an Order Establishing Appropriate Procedures, see supra note 6, that we direct FERC to compile a supplemental EIS, thereby taking into account the most recent information relevant to PG & E’s ability to provide energy to NCPA, NCPA’s own future electrical capacity, and future electrical demand in the NCPA service area.35 General*345ly, the initial decision whether a supplemental EIS is required should be made by the agency, not by a reviewing court. People Against Nuclear Energy v. NRC, 678 F.2d 222, 233-34 (D.C.Cir.1982), rev’d on other grounds sub nom. Metropolitan Edison Co. v. People Against Nuclear Energy, - U.S. -, 103 S.Ct. 1556, 75 L.Ed.2d 534 (1983). The record does not indicate that FOR ever presented a request to the Commission asking for supplementation of the EIS, although arguably FOR could have done so even after the close of administrative proceedings with respect to the license. See Michigan Consolidated Gas Co. v. FPC, 283 F.2d 204, 225 (D.C.Cir.1960). We need not consider the effect of FOR’s apparent failure to approach the Commission first, however, since we reject FOR’s request on its merits.
Under the Council on Environmental Quality’s NEPA Guidelines, an agency should prepare a supplemental EIS if there exists “significant new .. . information relevant to environmental concerns and bearing on the proposed action or its impacts.” 40 C.F.R. § 1502.9(c) (1981).36 This guideline does not mean that an agency must release and circulate a formal supplemental EIS, or a formal document explaining why the agency believes a supplemental EIS is unnecessary, every time some new information comes to light. Rather, a reasonableness standard governs. See California v. Watt, 683 F.2d 1253, 1268 (9th Cir.1982), cert. granted, - U.S. -, 103 S.Ct. 2083, 77 L.Ed.2d 295 (1983); Warm Springs Dam Task Force v. Gribble, 621 F.2d 1017, 1024 (9th Cir.1980); People Against Nuclear Energy v. NRC, 678 F.2d at 234 (expressly adopting the Warm Springs analysis); Humane Society of the United States v. Watt, 551 F.Supp. 1310, 1322 (D.D.C.1982), aff’d mem., 713 F.2d 865 (D.C.Cir.1983).
FOR’s new information, as we indicated earlier, see supra notes 6 & 7, appears to be of questionable value. Even if the information were somewhat more weighty, however, we would hesitate to command FERC to attend to it. CEC, as part of its continuing task of surveying California’s energy picture, issues new forecasts and predictions every few months, each soon to be superseded by the next. Were we to order the Commission to reassess its decisions every time new forecasts were released, we would risk immobilizing the agency. As the Supreme Court has admonished:
Administrative consideration of evidence ... always creates a gap between the time the record is closed and the time the administrative decision is promulgated [and, we might add, the time the decision is judicially reviewed],... If upon the coming down of the order litigants might demand rehearings as a matter of law because some new circumstance has arisen, some new trend has been observed, or some new fact discovered, there would be little hope that the administrative process could ever be consummated in an order that would not be subject to reopening.
Vermont Yankee Nuclear Power Corp. v. NRDC, 435 U.S. 519, 554-55, 98 S.Ct. 1197, 1217, 55 L.Ed.2d 460 (1978) (quoting ICC v. City of Jersey City, 322 U.S. 503, 514, 64 S.Ct. 1129, 1134, 88 L.Ed. 1420 (1944)). After prolonged consideration, FERC issued the CCWD license in 1982; review and reassessment of that decision, absent sufficient reason, should not continue indefinitely.
*346Conclusion
Our decision accords FERC no license to ignore requirements Congress has established for its decisionmaking process. We must hold the Commission, like all agencies, to a “strict standard of compliance” with NEPA. Calvert Cliffs' Coordinating Commission v. AEC, 449 F.2d 1109, 1112 (D.C.Cir.1971). But in this case, while FERC fell short of a formal requirement, its decision-making adequately responded to the concerns underlying NEPA. See Scenic Hudson Preservation Conference v. FPC, supra. We therefore decline to order a remand that would cause added delay and added cost to the public without genuinely advancing any purpose served by NEPA. Accordingly, the order of the Commission is
Affirmed.
A companion decision, issued today, resolves et al., Pacific Gas and Elec. Co. v. FERC, 720 F.2d 78.
. FERC took over the functions of the Federal Power Commission (FPC) on October 1, 1977, pursuant to 42 U.S.C. § 7172 (Supp. V 1981). The term “Commission” is used interchangeably in this opinion to refer to the FPC in actions prior to October 1, 1977, and to FERC thereafter.
. This was not the first license application filed in connection with the Calaveras project; CCWD initially applied for a license fifteen years earlier, in 1963, and applied again in 1975. The 1975 application was substantially revised to meet environmental objections, yielding the November 1978 application.
. Energy is the capability of doing work, e.g., lighting a light bulb. Energy is measured in gigawatt-hours (Gwh). The annual energy yield of an electric utility system is the total amount of electrical energy the system delivers in a year. The capacity of an electric utility system is the maximum amount of electrical energy the system can make available at any given moment of time. Capacity is measured in megawatts (MW).
Annual energy demand indicates the total amount of energy required in a year to satisfy consumers’ needs. Peak demand indicates the amount of energy required at those moments when consumers are using electricity at the highest rate. A utility is said to be capable of satisfying an area’s power needs if it can satisfy peak demand, that is, if its capacity equals or exceeds peak demand. See generally T. Sullivan & F. Heavner, Energy Reference Handbook (3d ed. 1981); California Energy Commission (CEC), Electricity Tomorrow, 1981 Final Report 17 — 18 [hereafter, Electricity Tomorrow],
If electrical generating plants could run continuously at full rated capacity, then plants capable of satisfying peak demand would necessarily be capable of satisfying the area’s overall energy needs as well; that is, they could produce an annual energy yield that equaled or exceeded the area’s annual energy demand. In fact, however, an electrical generating plant cannot run continuously at peak capacity; CEC assumes that each plant will generate only 65% of the energy it would generate if it could run at full capacity throughout the year. For this reason, it is not always the case that generating facilities capable of meeting peak demand will be capable of satisfying an area’s energy needs. Even though the generating facilities can supply the energy needed by the area at any isolated instant, they cannot perform at that level 24 hours a day, 365 days a year.
The area in which the Calaveras project will be located, however, is atypical in this respect: Peak demand there is unusually high compared to average demand, and the electric utility system, in order to satisfy peak demand, must have a great deal more capacity than is ordinarily found in systems with comparable overall energy needs. As a result, the capacity needed to meet peak demand is enough to assure generation of an annual energy yield exceeding the area’s annual energy demand even after taking into account the 65% assumption. Achieving the area’s power needs (by meeting peak demand) will thus mean achieving the area’s overall energy needs as well. See Electricity-Tomorrow 44.
. See Joint Appendix (J.A.) 631, 645 (power purchase contract between NCPA and CCWD); see also CEC Project Status Report No. 4, Staff Report, April, 1982 at 196 (100% of Calaveras power will go to NCPA); Affidavit of Robert E. Grimshaw, Oct. 27, 1982, at 1, attached to Motion of NCPA to Condense and Expedite Briefing Schedule and for Expedited Argument and Decision (same). The table cited by the dissent on this point, dissenting opinion at 111 n. 7, appears to contemplate sale of Calaveras power elsewhere only as part of one “ [alternative” possibility among many.
. Extensive proceedings took place as well before the California Water Resources Control Board, which approved and affirmed on rehearing the necessary water right permits for the project.
California agencies have taken various positions with regard to the project. Compare Comments of California Resources Agency, Feb. 11, 1980, reprinted in J.A. 410-11 (neither supporting nor opposing the project, but expressing concern as to “deficiencies” in the draft EIS), with CEC memorandum from Dale Nielsen to State Water Resources Control Board, Sept. 16, 1980, reprinted in J.A. 874-76 (finding the project “useful” and “attractive”).
. FOR concedes that FERC’s estimates of future demand were made on the basis of the most current information then available. Brief for Environmental Petitioners at 14 [hereafter, FOR Brief], FOR requests, however, that we order a reopening of the administrative record, pursuant to 16 U.S.C. § 8251 (b) (1976), so that still newer projections can be considered. See Application by Environmental Petitioners for Leave to Adduce Additional Evidence before FERC and Motion for an Order Establishing Appropriate Procedures. We deny this request on the ground that it does not “ ‘clearly appear that the new evidence would compel or persuade to a contrary result.’ ” Rocky Mountain Power Co. v. FPC, 409 F.2d 1122, 1128 n. 21 (D.C.Cir.1969) (quoting Louisville Gas & Elec. Co. v. FPC, 129 F.2d 126, 134 (6th Cir.), cert. denied, 318 U.S. 800, 63 S.Ct. 768, 87 L.Ed. 1164 (1942)). Throughout this proceeding FERC has used the latest electricity demand figures available to it; to allow the administrative process to function we must at some point call a halt to the parade of revised and further-revised studies. ICC v. City of Jersey City, 322 U.S. 503, 514, 64 S.Ct. 1129, 1134, 88 L.Ed. 1420 (1944).
The precise choice of projected growth rates to predict NCPA peak electrical demand, in any case, lacks overriding significance; the NCPA service area will face a more-than-200 MW shortfall in the years to come even if we assume a zero growth rate for the area. Further, the new evidence FOR cites hardly demonstrates that anticipated decline in PG & E’s overall demand is great enough to change significantly PG & E’s overall capacity needs. FERC has argued cogently that much of the “additional evidence” FOR would adduce is cumulative, unreliable, or not material. In sum, FOR has not demonstrated that the additional evidence it seeks to present would affect the outcome of the case. See Greene County Planning Bd. v. FPC, 559 F.2d 1227, 1233 (2d Cir.1976), cert. denied, 434 U.S. 1086, 98 S.Ct. 1280, 55 L.Ed.2d 791 (1978).
. FOR claims that by 1986 “a total of 339.99 MW of electricity is reasonably expected to occur by virtue of NCPA projected capacity additions.” FOR Brief at 16. FOR appears to have arrived at this figure, however, by including in its count the estimated capacities of almost every potential project listed in CEC flies with some predicted in-service date. The CEC Project Status Report data on which FOR draws encompass all proposed projects that *335have reached the stage of preliminary planning. There is no assurance that many of the projects listed will in fact be built. The Calaveras project, for example, is listed with a 1985 start-up date. Looking only to projects marked as in construction or operational — an approach within FERC’s expert discretion — we find only 140.4 MW of capacity scheduled to go in service by 1986. FERC’s 150 MW projection of NCPA’s generating capacity thus seems to be a generous one.
Even if we look to FOR’s most recent figures relating to NCPA capacity additions, material outside the agency record, we find no new information casting serious doubt on FERC’s calculations; this newest set of figures shows only 152.9 MW of capacity represented by NCPA projects beyond the planning stage.
. Federal and state views in this area do not always coincide, as one of the courses advocated by CEC illustrates. CEC urged repeal of federal laws prohibiting the burning of natural gas in electric power plants after 1989 so that California may continue to rely on gas-powered plants. See Electricity Tomorrow 386.
. See supra note 3.
. The PG & E resource plan projects 280 MW from “unidentified new large hydro projects from 1986 to 1992.” Electricity Tomorrow 276. The only new large hydroelectric installations in the PG & E planning area that appear likely to proceed are the SMUD/E1 Dorado Irrigation District SOFAR project (110 MW) and the Calaveras project. Id. The CEC Proposed Utility Resource Plan, 1980-1992, set out in Electricity Tomorrow 355, includes the Calaveras project. This plan is an “electricity sector scenario[]” drawn up by CEC staff that “corresponds to the utilities’ existing conservation programs and supply plans, adjusted to meet the Corn-mission’s adopted demand forecast instead of their own, somewhat higher forecasts.” Electricity Today 354. It sets out CEC’s prediction of what will happen given current utility planning. See also infra note 11.
. This estimate comes from the Harry Allen-Warner Valley Energy System Staff Report, released by CEC in March 1981, J.A. 969, 973; the report includes 200 MW from the Calaveras project as “reasonably expected” power. J.A. 977.
. For an illustration of planning uncertainties, see Electricity Tomorrow 51-54, which compares model 1980-1992 electricity demand projections made by PG & E and by CEC for the PG & E planning area. Both models predict populations for the planning area, and arrive at somewhat different figures. Both attempt to project changes in area economic activity, since power consumption is correlated with that variable. PG & E’s model uses “measures of wage income, taxable sales, and industrial production.” Id at 51. CEC’s model considers “future employment in 30 different industries, wages and value added in 18 industries, future bond interest rates, construction costs, and macroeconomic variables such as GNP and California per capita income.” Id Both models project future prices of electricity in different sectors, and reach different results. Both attempt to predict the price of fuels such as natural gas that, in some uses, may substitute for electricity. Both attempt to assess the degree to which conservation will curtail demand.
Should the Commission attempt to widen its examination to encompass ever larger areas, it could not rely on existing studies of smaller regions; piecing together studies limited to smaller regions would ignore the interconnections and synergistic effects a study of the larger area would show. Cf. Kleppe v. Sierra Club, 427 U.S. 390, 409-10, 96 S.Ct. 2718, 2729-30, 49 L.Ed.2d 576 (1976) (recognizing that segmentation of an environmental investigation may slight “cumulative or synergistic environmental impact”). The Commission’s task, if it were to embark on a grand-scale projection adventure of its own, would be arduous indeed.
. Lee, The Path Along The Ridge: Regional Planning in the Face of Uncertainty, 58 Wash.L. Rev. 317, 317 (1983).
. Id. at 318-19 (italics in original). Professor Lee reports:
If the growth rate [in the Northwest region] differs by only 0.3% per year from the anticipated rate, the gap between the anticipated load and actual load will amount to the equivalent of a nuclear plant in less than fifteen years. Our present ability to forecast demand falls considerably short of even this 0.3% criterion.
Id. at 318 (footnotes omitted).
. There is no end to this type of exchange. As far as FERC may look, a challenger can allege that electric power is available in abundance from sources outside the circle FERC has drawn.
. We note that in Mason County Medical Ass’n v. Knebel, 563 F.2d 256 (6th Cir.1977), the court apparently endorsed the Rural Electrification Administration’s conclusion that the utility in question “should [not] be ‘dependent on ... others for a disproportionate amount of its capacity requirements.’ ” Id. at 263 (quoting the EIS).
. Justice Douglas discussed the “vast commercial implications,” 387 U.S. at 440, 87 S.Ct. at 1718, of fishing on the river, and expressed his concern that the effects of the Commission-approved project on nearby salmon runs might lead to the destruction of “a great industry and a great ‘recreational’ asset of the Nation.” Id: at 442, 87 S.Ct. at 1719. He observed that Congress had “established] a national policy of ‘recognizing the vital contribution of our *339wildlife resources to the Nation,’ ” id. at 443, 87 S.Ct. at 1720, (quoting the Fish and Wildlife Coordination Act, 16 U.S.C. § 661 (1976)), and characterized fish and wildlife as “all-important” to the decision. Id. at 444, 87 S.Ct. at 1720. He concluded:
The question whether the proponents of a project “will be able to use” the power supplied is relevant to the issue of the public interest. So too is the regional need for the additional power. But the inquiry should not stop there---- [A decision to grant a license] does not, of course, turn simply on whether the project will be beneficial to the licensee. Nor is the test solely whether the region will be able to use the additional power. The test is whether the project will be in the public interest. And that determination can be made only after an exploration of all issues relevant to the “public interest,” including future power demand and supply, alternate sources of power, the public interest in preserving reaches of wild rivers and wilderness areas, the preservation of anadromous fish for commercial and recreational purposes, and the protection of wildlife.
Id. at 450, 87 S.Ct. at 1724. In dissent, Justice Harlan said that the Court had “substituted its own preferences for the discretion given by Congress to the ... Commission.” Id. at 454, 87 S.Ct. at 1726. He noted that the second part of the Court’s opinion took on an issue that no party had pressed the Court to consider. Id. at 454-55 & n. 7, 87 S.Ct. at 1726 & n. 1.
. See supra pp. 97-98.
. Scenic Hudson Preservation Conference v. FPC, 354 F.2d 608 (2d Cir.1965), cert. denied, 384 U.S. 941, 86 S.Ct. 1462, 16 L.Ed.2d 540 (1966), contains nothing to the contrary. In that case, it appears that the Commission had never at any point seriously considered the possibility of the applicant’s purchasing power from any other utility in lieu of building the proposed plant.
. Arguments raised by FOR under NEPA that go to the substantive validity of FERC’s decision are misplaced. See Strycker’s Bay Neighborhood Council v. Karlen, 444 U.S. 223, 100 S.Ct. 497, 62 L.Ed.2d 433 (1980).
. CCWD plans eventually to take further steps towards utilization of the North Fork Stanislaus River for purposes of irrigation, water supply, and provision of recreational facilities. It has identified potential water-related projects in each area of Calaveras County, J.A. 201, and revenues from the hydroelectric project may make it possible to build some of these. New reservoirs, canals, or pipelines some day built by CCWD may well be related to projects then in place, including the Calaveras project.
However, when this matter was before the Commission, CCWD had not settled on construction of any particular water supply project, and construction of the Calaveras project does not lock CCWD into a water supply project commitment. The determination of when various projects in an area are sufficiently concrete and closely related so as to require the filing of a single comprehensive EIS is a difficult one, “properly left to the informed discretion of the responsible federal agencies.” Kleppe v. Sierra Club, 427 U.S. at 412, 96 S.Ct. at 2731. FERC’s decision to treat the Calaveras project separately from any potential but yet unscheduled CCWD water supply project was in no respect unreasonable. Kleppe; see also Izaak Walton League of America v. Marsh, 655 F.2d 346, 374-75 & nn. 73-74 (D.C.Cir.), cert. denied, 454 U.S. 1092, 102 S.Ct. 657, 70 L.Ed.2d 630 (1981).
.NEPA was passed in 1969, two years after the Udall decision. See generally Scenic Hudson Preservation Conference v. FPC, 407 U.S. 926, 927-28, 92 S.Ct. 2453, 2454, 32 L.Ed.2d 813 (1972) (Douglas, J., dissenting from denial of cert.).
. Cf. North Slope Borough v. Andrus, 642 F.2d 589, 602 (D.C.Cir.1980) (“[T]he very concept of ‘alternatives analysis’ is problematic as applied to an evaluation of lease stipulations”); Conservation Law Found. v. Andrus, 623 F.2d 712, 717 (1st Cir.1979) (“Appellants assert a failure to determine the cost of the alternative of ‘no action,’ i.e., not proceeding with the lease sale. [That claim is] at best strained. The cost of the alternative of not proceeding is obvious — any oil which might be found will not be found.”).
. Swinomish Tribal Community v. FERC, 627 F.2d 499, 514-15 (D.C.Cir.1980). In that case, without extended discussion, we found petitioners’ “power purchasing alternative” NEPA claim to be without merit; we quoted approvingly the Commission’s conclusion that “the purchase of power from the Bonneville Power Administration is subject to what we consider to be an unassured sufficiency of capacity, and certainly energy, existing in the Pacific Northwest.” Id. at 515.
. See also North Slope Borough v. Andrus, 642 F.2d 589, 600-01 & n. 47 (D.C.Cir.1980); Environmental Defense Fund v. TVA, 492 F.2d 466, 468 n. 1 (6th Cir.1974) (administrative practicality bears on “alternatives” appropriately considered).
. National Wildlife Found. v. Andrus, 440 F.Supp. 1245 (D.D.C.1977), is not to the contrary. The court held in that case, as a subsidiary matter, that a blanket, out-of-hand rejection of power purchasing without any investigation violated NEPA.
We note that for NEPA purposes, we do not place weight on the relative size of the project proposed by CCWD. See Metropolitan Edison Co. v. People Against Nuclear Energy, - U.S. -, 103 S.Ct. 1556, 1563, 75 L.Ed.2d 534 (1983).
. The July 1982 order was not circulated for comment before the final decision was made, but “in light of comments [previously] submitted ... additional comment ... would not likely produce additional light for the decision makers.” Environmental Defense Fund v. Froehlke, 368 F.Supp. 231, 237 (W.D.Mo.1973), aff’d sub nom. Environmental Defense Fund v. Callaway, 497 F.2d 1340 (8th Cir.1974).
. Cf. North Slope Borough v. Andrus, 642 F.2d 589, 603-04 & n. 78 (D.C.Cir.1980) (court examined documents other than the EIS to clarify agency decisionmaking process; examination involved “no elements of information withholding, or post hoc rationalization”).
. Cf. International Harvester Co. v. Ruckelshaus, 478 F.2d 615, 650 n. 130 (D.C.Cir.1973) (EPA may deny petitions for suspension of automobile emissions standards without filing EIS; “[t]o require a ‘statement,’ in addition to a decision setting forth the same [environmental] considerations, would be a legalism carried to the extreme”); Wyoming v. Hathaway, 525 F.2d 66, 72 (10th Cir.1975) (court upheld EPA cancellation of chemical toxicant registrations in part on ground that agency “order, findings and conclusions substantially complied with ... NEPA”), cert. denied, 426 U.S. 906, 96 S.Ct. 2226, 48 L.Ed.2d 830 (1976).
. See also California v. Watt, 683 F.2d 1253, 1268 (9th Cir.1982) (court relied on study prepared by agency in finding that supplemental EIS was unnecessary), cert. granted, - U.S. -, 103 S.Ct. 2083, 77 L.Ed.2d 295 (1983); Environmental Defense Fund v. Andrus, 619 F.2d 1368 (10th Cir.1980) (careful studies prepared by agency obviated need for formal supplementation of programmatic EIS before taking site-specific action).
. When the court in Swinomish turned to consideration of the adequacy under NEPA of FERC’s investigation of power purchasing, see supra note 24, it again relied heavily on language in the Commission’s opinion denying rehearing. 627 F.2d at 514-15.
. See 1-291 Why? Ass’n v. Burns, 372 F.Supp. 223 (D.Conn.1974) (environmental decisionmaking was done only post hoc, after the agency’s crucial decision was made, and the information on which the agency relied was not made public), aff'd, 517 F.2d 1077 (2d Cir.1975); NRDC v. Morton, 337 F.Supp. 170 (D.D.C.1972) (data relating to environmental concerns was compiled by agency after the start of litigation, and filed only with the court; case declared moot on other grounds).
. See Grazing Fields Farm v. Goldschmidt, 626 F.2d 1068 (1st Cir.1980) (evidence of the agency’s environmental decisionmaking scattered throughout the record in non-useful form).
. Calvert Cliffs’ Coordinating Comm. v. AEC, 449 F.2d at 1113 (quoting Hearings on S. 1075, S. 237, and S. 1752 Before the Senate Comm, on Interior and Insular Affairs, 91st Cong., 1st Sess. 116 (1969) (statement of Sen. Jackson)).
. We consider in relation to FOR’s supplemental EIS argument only information that came into existence too late to be considered by FERC in its July 1982 order. For reasons set forth earlier in this opinion, we decline to remand so that the Commission can prepare a supplemental EIS incorporating information published after the EIS was filed, but in fact considered by FERC. in preparing the July 1982 order.
*345The inquiry we make at this point differs, in form at least, from the one we undertook under 16 U.S.C. § 8251(b), supra note 6. There the question was whether the new evidence offered by FOR was so compelling that we were obligated to exercise our discretion to order the Commission to reopen its record and reconsider its decision under the FPA. Here the question is whether there exists new information relevant to environmental concerns so significant that it was an abuse of discretion for the agency itself, when the information became available, not to reassess its environmental decisionmaking under NEPA.
. The Guidelines are “entitled to substantial deference” as an interpretation of NEPA, Andrus v. Sierra Club, 442 U.S. 347, 358, 99 S.Ct. 2335, 2341, 60 L.Ed.2d 943 (1979), and their instructions regarding supplementation of the EIS have been followed in this circuit. See, e.g., People Against Nuclear Energy v. NRC, 678 F.2d at 233.