There is hereby levied a tax at the rate levied on gasoline and gasohol on liquid alternative fuel used to operate a highway vehicle by means of a vehicle supply tank that stores fuel only for the purpose of supplying fuel to operate the vehicle. There is hereby levied a tax at a rate equivalent to that levied on gasoline and gasohol on all other alternative fuel used to operate a highway vehicle. The Commissioner shall determine the equivalent rate applicable to such other alternative fuels.