Oregon Revised Statutes Trade Regulations and Practices § 646.935

(1) No person operating a service station selling to the public at retail diesel fuel, where delivery is regularly made into a receptacle on a vehicle from which receptacle the fuel is supplied to propel the vehicle, shall refuse to sell and deliver any quantity of such fuel to any vehicle during regular business hours, upon demand and tender of the posted price plus any applicable tax for such fuel delivered, subject to a rationing policy established by state or federal statute or regulation.

(2) A price differential or method of delivery designed to discriminate against or discourage purchases by vehicles of small fuel capacity is prohibited. However, a reasonable discount or differential based upon quantity of delivery shall not be considered discriminatory.