Okla. Stat. tit. 52 § 110
In any proceeding or at any hearing before the Commission wherein the Commission shall require or shall deem it advisable to ascertain and/or find the reasonable market demand and/or the transportation or marketing facilities for oil that may be produced from any common source of supply during any specific period of time thereafter, it shall be competent, subject to such limitations and conditions, as shall be prescribed and provided by general order or rule of the Commission, to receive in evidence in such proceeding or at such hearing, any statement which shall have been communicated to (a) the Commission, or (b) to the Secretary of the Commission, or (c) to the Proration Umpire, by any purchaser or taker of oil by (a) telegram, or (b) letter, which shall state the amount of oil produced from said common source of supply (a) that such purchaser or taker contemplates or intends he or it will purchase during the period of time involved; or (b) the capacity of his or its transportation or marketing facilities which will be, during the period of time involved, available for transportation and/or marketing oil that may be produced from such common source of supply; and the Commission in ascertaining and determining the transportation or marketing facilities, or the reasonable market demands for oil during any such period of time that may be produced from such common source of supply may give such weight to such evidence that it shall determine the same is entitled.
Okla. Stat. tit. 52, § 110