Okla. Stat. tit. 52 § 240
Every person, firm or corporation, now or hereafter engaged in the business of purchasing and selling natural gas in this state, shall be a common purchaser thereof, and shall purchase all of the natural gas which may be offered for sale, and which may reasonably be reached by its trunk lines, or gathering lines without discrimination in favor of one producer as against another, or in favor of any one source of supply as against another save as authorized by the Corporation Commission after due notice and hearing; but if any such person, firm or corporation, shall be unable to purchase all the gas so offered, then it shall purchase natural gas from each producer ratably. It shall be unlawful for any such common purchaser to discriminate between like grades and pressures of natural gas, or in favor of its own production, or of production in which it may be directly or indirectly interested, either in whole or in part, but for the purpose of prorating the natural gas to be marketed, such production shall be treated in like manner as that of any other producer or person, and shall be taken only in the ratable proportion that such production bears to the total production available for marketing. The Corporation Commission shall have authority to make regulations for the delivery, metering and equitable purchasing and taking of all such gas and shall have authority to relieve any such common purchaser, after due notice and hearing, from the duty of purchasing gas of an inferior quality or grade.
Okla. Stat. tit. 52, § 240