The question presented in this case is whether under the Natural Gas Act, 52 Stat. 821, 15 U.S.C. § 717 et seq., 15 U.S.C.A. § 717 et seq., a regulated natural gas company furnishing gas to a distributing company under a long-term contract may, without the consent of the distributing company, change the rate specified in the contract simply by filing a new rate schedule with the Federal Power Commission. The pertinent provisions of the Act are set forth in the margin.
Respondent Mobile Gas Service Corporation (Mobile), a distributor of natural gas to domestic and industrial users in Mobile, Alabama, acquires its gas from petitioner United Gas Pipe Line Company (United), a 'natural-gas company' subject to regulation under the Act. In 1946 the Ideal Cement Company (Ideal), planning to construct a cement plant in the city provided it could be assured a supply of gas at a sufficiently low rate, obtained from Mobile an agreement to furnish gas for a 10-year term at 12 cents per MCF (thousand cubic feet). Mobile, in turn, before entering into a contract with Ideal, obtained from United a 10-year contract to supply gas for resale to Ideal at the equivalent of 10.7 cents per MCF, a rate substantially lower than that for other gas furnished by United. This contract was filed with the Federal Power Commission as an amendment to the general supply contracts between Mobile and United, and, with the approval of the Commission, became a part of United's filed schedules of rates and contracts.
In June 1953 United, without the consent of Mobile, filed new schedules with the Commission which purported to increase the rate on gas for resale to Ideal to 14.5 cents per MCF, a rate more closely approximating that for other gas furnished to Mobile by United. Claiming that United could not thus unilaterally change the contract rate, Mobile petitioned the Commission to reject United's filing. The Commission denied the petition, holding that under § 4(d) of the Act the new rate, being a non-suspendible industrial rate, automatically became effective 30 days after filing and would remain in effect unless and until the Commission should, after investigation under § 4(e), determine the new rate to be unlawful. Mobile paid the new rate until April 15, 1955, when United, with Commission approval, accepted an assignment to it of Mobile's contract with Ideal. This assignment made the pending investigation into the lawfulness of the new rate moot, since in the Commission's view its determination on that matter would have no retroactive effect. Thus the only question before us is whether United property collected from Mobile the difference between the old 10.7-cent rate and the new 14.5-cent rate during the period from July 25, 1953 (when the new rate purportedly went into effect), to April 15, 1955 (when United took over the Ideal contract)-a sum aggregating approximately $240,000. On Mobile's petition for review, the Court of Appeals for the Third Circuit (Hastie, J., dissenting) reversed the Commission's order, directed it to reject United's filing of the new schedule insofar as it purported to increase the rate in question, and held Mobile entitled to a return of the amounts paid in excess of the contract rate. 215 F.2d 883. Both the Commission and United, which had intervened in the Court of Appeals, petitioned for certiorari, which we granted because of the importance of this question in the administration of the Natural Gas Act. 348 U.S. 950, 75 S.Ct. 446, 99 L.Ed. 742. For the reasons discussed below, we hold that the Natural Gas Act does not give natural gas companies the right to change their rate contracts by their own unilateral action.