The tax levied and imposed shall be measured and determined by the number of gallons of gasoline and diesel fuel so imported and actually used on the highways of this state. No gasoline or diesel fuel on which the tax levied by the Motor Fuel Tax Code has been paid to this state shall be used in computing the tax imposed by this section. In the event the tax levied by this section can be more accurately determined on a mileage basis, that is, by determining and using the total number of miles traveled in Oklahoma, or in case it is practicable to so determine the tax, the Corporation Commission is authorized to accept and approve such basis.
Okla. Stat. tit. 68, § 603