Wash. Rev. Code § 78.52.345
Each person now or hereafter purchasing or taking for transportation oil from any owner or producer shall purchase or take ratably without discrimination in favor of any owner or operator over any other owner or producer in the same pool offering to sell his or her oil produced therefrom to that person. If the person purchasing or taking for transportation oil does not have need for all such oil lawfully produced within a pool, or if for any reason is unable to purchase all of the oil, then it shall purchase from each operator in a pool ratably, taking and purchasing the same quantity of oil from each well to the extent that each well is capable of producing its ratable portion without waste. Nothing in this section may be construed to require any owner or operator to sell his or her product to only one purchaser or to require more than one pipeline connection for each producing well. If any such purchaser or person taking oil for transportation is likewise an operator or owner, the purchaser or person is prohibited from discriminating in favor of his or her own production, or production in which he or she may be interested, and his or her own production shall be treated as that of any other operator or owner.
RCW 78.52.345