Opinion for the Court filed by Circuit Judge WALD.
The Federal Energy Regulatory Commission (“Commission”) appeals from a decision of the district court holding that the appropriate interest rate to be applied to refund obligations incurred by Triton Oil and Gas Corporation (“Triton”) under thе refund requirements of the Commission’s Opinion No. 598 1 is the 7% interest rate specified in Opinion No. 598 and not the Commission’s general, higher rate of interest established in its regulations, 18 C.F.R. § 154.102(c)(2) (1984), issued subsequent to Opinion No. 598. We affirm the district court.
I. Background
We have already set forth a detailed account of the facts and intricate procedural background of this case in
Federal Energy Regulatory Commission v. Triton Oil & Gas Corp.,
II. Discussion
The sole issue on appeal is whether the district court erred in finding Triton’s refund obligations subject to the 7% interest rate prescribed in Opinion No. 598 and not the higher rate established by the Commission’s current regulations. In rejecting the Commission’s claim that Triton’s refund obligations were subject to the Commission’s current regulation establishing a fluctuating interest rate tied to market conditions, the district court relied on the fact that the Commission itself has indicated that the 1% interest rate applies to refunds made pursuant to Oрinion No. 598. See J.A. at 230. Indeed each time the Commission has incorporated new, higher interest rates in its general rules, subsequent to the issuance of Opinion No. 598, it has provided that the new rates would not be applicable to refunds made under Opinion No. 598.
The Commission first sought to increase its general interest rate from 7% to 9% in Order No. 513, 52 F.P.C. 920 (1974). This order was reversed and remanded, however, in
American Public Gas Association v. FPC,
Where there is a final non-appealable Commission order directing the disbursement of refunds of amounts collected or held during the time periods which are the subject of this order, the Commission does not intend to reconsider or modify thоse individual orders. The orders will stand as issued.
56 F.P.C. at 290.
In a subsequent order denying a rehearing and clarifying Order No. 513-A, the Commission specifically clarified the status of Opinion No. 598 stating:
In Opinions 598 and 662, a final, nonappealable order has been issued as to the interest rate to be paid on the amount of refunds to be subsequently determined, and the provision in Order No. 513-A regarding final and non-appealable orders applies. 56 F.P.C. 2332,2336 (1976). 3 The Commission denied a petition for rehearing of this clarifying оrder, 56 F.P.C. 3402 (1976), 4 and its decision was affirmed by this court in Northern Illinois Gas Co. v. FERC, 575 F.2d 920 (D.C.Cir.1978).
Thereafter, the Commission issued Order No. 47, effective October 1, 1979, increasing the interest rate on refunds from 9% to the current fluctuating prime rate. [1977—1981 Transfer Binder] FERC Reg. Preambles (CCH) 1130,083,
5
aff'd, United Gas Pipe Une Co. v. FERC,
[T]he rates of interest prescribed by Order No. 47 will not apply where a different stipulated rate of interest has been established by court order, or by a Commission order approving a settlement agreement which became final and nonappealable by September 10, 1979.
Id. at 30,837. As recently as April 30, 1984, the Commission reaffirmed the non-applicability of its current interest rates to refunds required under Opinion No. 598. See Disputed Zone Offshore Louisiana, 27 F.E.R.C. ¶61,166 (1984). 6
The foregoing discussion readily illustrates that the Commissiоn’s assertion that its current interest rate is applicable to Triton’s refund obligations under Opinion No. .598 is totally inconsistent with the Commission’s orders establishing interest rates on refunds and its implementation of those orders in other administrative proceedings.
7
See supra
notes 4 & 6. The Commission seeks to justify its departure from its past practice by arguing that the imposition of interest on refunds is a means of preventing unjust enrichment, and that Triton will be unjustly enriched if it is not required to pay its refund obligations under Opinion No. 598 at the Commis
The Commission, nevertheless, urges this court to hold that the 7% interest rate established in Opinion No. 598 for producer refunds was predicated upon producers effecting prompt compliance and that Triton’s unreasonable delay in effecting compliance warrants imposition of the current interest rate on Triton’s refund obligation. Brief for Commission at 17-18. Triton rеsponds that it reasonably believed it had no refund obligation under Opinion No. 598 and that it should not be penalized for seeking a determination of the existence vel non of its refund obligation. See Brief for Triton at 15-16. The district court was persuaded by Triton’s argument stating: “Triton should not bе penalized for the reasonable exercise of its right to judicial review by having to pay a rate of interest higher than that mandated by Opinion 598.” J.A. at 230. Under the circumstances of this case, we cannot say Triton’s delayed compliаnce was unreasonable or unwarranted. An earlier opinion of the district court filed July 27, 1982, found that Triton had no obligations under Opinion No. 598. See J.A. at 144-55. Although in Triton I we reversed the holding of the district court, Triton’s arguments were neither frivolous nor completely laсking in merit. 9
The Commission’s assertion that Triton’s refund obligations under Opinion No. 598 should be subject to the Commission’s current fluctuating prime rate is a clear departure from the Commission’s rules and past practices for which the Commission has given no valid justifiсation. We, therefore, affirm the district court’s order requiring Triton to make refunds at the 7% simple interest rate specified in Opinion No. 598.
Affirmed.
Notes
. Opinion No. 598, 46 F.P.C. 86, issued on July 16, 1971, and was later modified in Opinion No. 598-A, 46 F.P.C. 633 (1971). These opinions approved a settlement agreement establishing ceiling rates for producer sales of natural gas in the Southern Louisiana area and imposing refund obligations of approximately $150,000,000. See Brief for Commission at 5. Both opinions were affirmed by the Fifth Circuit in
Placid Oil Co. v. FPC,
. Specifically, 18 C.F.R. § 154.102(c)(2)(iii)(A) (1984) establishes the following formula for computing interest:
At an average prime rate for each calendar quarter on all excessive rates or charges held (including all interest apрlicable to such rates or charges) on or after October 1, 1979. The applicable average prime rate for each calendar quarter shall be the arithmetic mean, to the nearest one-hundredth of one pеrcent, of the prime rate values published in the Federal Reserve Bulletin, or in the Federal Reserve’s "Selected Interest Rates" ..., for the fourth, third, and second months preceding the first month of the calendar quarter.
(B) The interest required to be paid under parаgraph (c)(2)(iii)(A) of this section shall be compounded quarterly.
. The Commission set forth the following rationale for its position:
The practical reason for drawing a distinction is the importance of having conclusive, final judgments upon which thе parties to a proceeding may rely without fear that at some later point the terms agreed to or relied upon will be subject to change. In the interests of such finality, the Commission has determined that it is reasonable and non-discriminаtory to make a distinction in the application of Order No. 513-A on the basis of whether a final, non-appealable order has been issued in a proceeding ____
56 F.P.C. at 2334 (1976).
. In its order denying the rehearing, the Commission noted that it had reaffirmed its pоlicy of not reconsidering interest rates established in final, nonappealable orders in several recent orders denying petitions requesting imposition of the new 9% rate. See 56 F.P.C. at 3404 & n. 6 (citing Texas Eastern Transmission Corp., 56 F.P.C. 2877 (1976); Northern Natural Gas Co., 56 F.P.C. 2870 (1976); Columbia Gas Transmission Corp. and Columbia Gulf Transmission Co., 56 F.P.C. 2678 (1976); Cities Service Gas Co., 56 F.P.C. 2669 (1976)).
. Codified at 18 C.F.R. § 154.102(c)(2) (1984).
. One of the questions in
Disputed Zone Offshore Louisiana
was what interest rate should be applied to refunds under Opinion No. 598 where such refunds had been held in abeyance pending resolution of a boundary dispute between federal and state authority. The Commission stated that with respect to refunds under Opinion No. 598, all the terms of the settlement agreement approved in that opinion apply including the 7% interest rate.
See
27 F.E.R.C. at 61,305. The Commission seeks to distinguish
Disputed Zone
by claiming that whereas in
Disputed Zone
liability for the refunds was not finally established until the boundary disрute was settled in
United States v. Louisiana,
. The Commission adhered to its past practice in its initial complaint in the present case requesting only 7% interest. See J.A. at 8. It was not until after this court’s decision in Triton I, and Triton’s submission to the district court, on remand, of its computations of principal and interest due that the Commission for the first time requested interest calculated in accordance with its current regulations. See J.A. at 167-73.
. The Commission cites
Shell
as supporting its argument that persons who unreasonably delay making refunds run the risk of interest rates increasing.
See
Brief for Commission at 21. The court in
Shell,
however, clearly distinguished cases covered by Opinion No. 598: Whereas
Shell
involved refunds by pipeline purchasers to producers, Opinion No. 598 is expressly applicable only to refunds by producers to pipeline purchasers.
It is important to note that Opinion No. 598 was the adoption of a settlement agreement ... [and] [t]he interest rate was locked in because it was part of a settlement agreement.664 F.2d at 80 n. 1.
. The Commission asserts that Triton did not exercisе its right to judicial review of Opinion No. 598 and that its refund obligation became final in 1974 with the Supreme Court’s affirmance in
Mobil Oil Corp. v. FPC,
The Commission also asserts,
see
Reply Brief for Commission at 4-5, that Triton's position was unreasonable because the Commission had dispositively addressed the exact question upon which Triton based its contention that it had no refund obligation in an order issued sixteen months after Opinion No. 598.
See
Area Rate Proceeding ..., 48 F.P.C. 980 (1972) (interpreting Opinion No. 598 to require refunds whatever the nature of the certificate under which a producer was collecting charges). The Commission’s order, however, only addressed one of three issues raised by Triton in
Triton I,
and in
Triton I
while we gave "some weight” to the
