concurring specially:
I join in the decision of the majority to affirm the judgment of the district court. On the issue concerning retroactivity of Ruling 1974-28, however, I would do so on different grounds. The majority holds that Caribou cannot assert retroactivity as a defense because the defense did not exist at *1267the time of the transaction between the parties. I would instead recognize Caribou’s position as a colorable defense, but would hold that the FEA action is valid in this case.
In order to understand the difference between my position and the majority’s, it is necessary to first explicate Caribou’s argument. Caribou contends that the stripper well exemption was never intended to exempt condensate produced from gas wells, and that therefore, after the date of its passage, all condensate produced from these wells should have been sold at a controlled price. Caribou makes this contention in spite of the fact that until the passage of Ruling 1974-28, the commercial practice in the industry was to sell gas well condensate at the “premium price.” This industry practice ended with the promulgation of Ruling 1974-28 which required this condensate to be sold at the controlled price.
In September 1975, the FEA decided that Ruling 1974-28 would only be applied prospectively. The effect of this 1975 change, according to Caribou, was to legitimate those sales of gas well condensate at “premium prices” which had occurred from the time of the passage of the stripper well' exemption until the time of the promulgation of Ruling 1974-28. Therefore, by sanctioning “premium prices” for this period in the face of Congressional intent that these prices be controlled, the 1975 change retroactively changed the law for this period.
The essence of the majority analysis is that Caribou cannot assert retroactivity as a defense because the challenged FEA action, Ruling 1974-28, was promulgated subsequent to the transactions between the two parties. Therefore, Caribou asserts a defense that did not exist at the time of these transactions.
I believe instead that Caribou argues that Ruling 1974-28, in stating that the exemption applied only to oil well condensate, merely clarified, but did not change the law. From this perspective, the September 1975 amendment was, in effect, a decision to not enforce the law until 1975. As such, the September 1975 ruling pulled the rug out from under Caribou by eliminating its defense to Sohio’s contract claim. The real issue in this case, then, centers around the validity of the 1975 ruling. The validity of this ruling is legitimately challenged regardless of the fact that it was handed down after all dealings between the companies had ended.
Though I agree that the validity of the September 1975 ruling is properly contested in the present proceeding, I cannot agree that it is subject to challenge on grounds of retroactivity. The September 1975 ruling seeks a prospective, not retroactive, application of Ruling 1974-28. Ironically, the result which Caribou advocates is in itself a retroactive application of Ruling 1974-28.
The real issue in this case is whether the FEA had the authority to issue a ruling prospectively when the effect of the ruling was to change, retroactively, the “true intent” of a statute of Congress. Caribou argues that Congress intended for the exemption to apply only to oil wells and that the exemption should have been so applied from its inception. I agree that if the meaning of the statute was clear, the FEA would have had no power to take gas well condensate from the exemption without complying with § 753(g)(2), for to do so would have rendered the 1975 ruling invalid. The principal defect of this course of action would not be a retroactive change of the statute, so much as the failure of the FEA to conform to the statutory scheme created by Congress.
The weakness of Caribou’s argument finally rests with the fact that it is impossible to fathom the “true intent” of the stripper well exemption. The provision is ambiguous on its face for it exempts crude oil produced “from any lease.” 15 U.S.C. § 753(e)(2)(A) (Supp.1975). The statute does not define the key words such as “crude oil” and “lease.” Therefore, it is impossible to tell whether the statute applies to gas well leases.
I would hold that because the statute is unclear, it was the province of the FEA to interpret the scope of the stripper well lease exemption created by Congress. In so do*1268ing it was natural for the FEA to seek out the intent of the drafters of the Act. The FEA believed that Congress had intended the exemption to apply only to oil wells. The fact that the FEA based Ruling 1974-28 upon this perception did not of itself vitiate the agency’s power to choose whether to enforce the ruling retroactively or prospectively only.
It is clear that an agency has the power to enforce its decision prospectively. Lodges 743 and 1746 v. United Aircraft Corp., 534 F.2d 422, 452-53 (2d Cir. 1975); NLRB v. Q-T Shoe Manufacturing Co., 409 F.2d 1247, 1250-52 (3d Cir. 1969); Joseph v. FCC, 131 U.S.App.D.C. 207, 212, 404 F.2d 207, 212 (1968). In fact, courts have examined more closely those agency decisions given retroactive effect because of the increased likelihood of these rulings to unduly prejudice a party. NLRB v. Q-T Shoe Manufacturing Co., supra, 409 F.2d 1252.
The decision of whether retroactively to apply a newly adopted administrative rule rests within the sound discretion of the agency, after considering the following factors:
(1) whether the particular case is one of first impression, (2) whether the new rule represents an abrupt departure from well established practice or merely attempts to fill a void in an unsettled area of the law, (3) the extent to which the party against whom the rule is applied relied on the former rule, (4) the degree of the burden which a retroactive order imposes on a party, and (5) the statutory interest in applying a new rule despite reliance of a party on the old standard.
Retail, Wholesale and Department Store Union v. NLRB, 151 U.S.App.D.C. 209, 219, 466 F.2d 380, 390 (1972). I see no reason why a different standard should govern the decision of the FEA to enforce its interpretation of the stripper well exemption only prospectively.* I would hold that the FEA did not abuse its discretion in making this decision and that the September 1975 ruling is therefore valid.
I concur in the result.
Most of the cases dealing with the power of an agency to enforce a ruling prospectively deal with legislative rulemaking instead of the interpretative rulemaking involved in this case. For this reason, there is a dearth of case law on the precise question presented in this appeal — the . validity of a prospective interpretative rule. One leading commentor on administrative law argues that an agency should have the power to limit an interpretative ruling to prospective effect. See K. Davis, 1 Administrative Law 353 (1958). He also describes one instance where this power was utilized. In 1938, the Wage and Hour Administrator of the Fair Labor Standards Act issued an interpretative bulletin which stated that the Act was not meant to cover plants where the employees worked on raw materials derived from within the state and where none of the products of the plant moved in interstate commerce. Subsequently, two court decisions, Chapman v. Home Ice Co., 136 F.2d 353 (6th Cir. 1943) and Hamlet Ice Co. v. Fleming, 127 F.2d 165 (4th Cir.), cert. denied, 317 U.S. 634, 63 S.Ct. 29, 87 L.Ed. 511 (1942), held that the Act covered these plants. The Administrator accordingly amended his interpretative bulletin to comply with the decision but expressly provided that the amendment would apply only after a specified future date. See Davis, supra.