Oregon Revised Statutes Revenue and Taxation § 319.530

(1) To compensate this state partially for the use of its highways, an excise tax hereby is imposed at the rate of 30 cents per gallon on the use of fuel in a motor vehicle.

(2) Except as otherwise provided in subsections (3) and (4) of this section, 100 cubic feet of fuel used or sold in a gaseous state, measured at 14.73 pounds per square inch of pressure at 60 degrees Fahrenheit, is taxable at the same rate as a gallon of liquid fuel.

(3) One hundred twenty cubic feet of compressed natural gas used or sold in a gaseous state, measured at 14.73 pounds per square inch of pressure at 60 degrees Fahrenheit, is taxable at the same rate as a gallon of liquid fuel.

(4) One and three-tenths liquid gallons of propane at 60 degrees Fahrenheit is taxable at the same rate as a gallon of other liquid fuel.