10-47B-176. Determining tax liability of interstate fuel user licensee--Overpayment refund. The tax liability of an interstate fuel user licensee shall be determined based on average fuel consumption for all qualified vehicles operated by the licensee within this state. Average fuel consumption is equal to the total fleet vehicle miles traveled divided by total fleet gallons of fuel consumed to calculate an average mile per gallon (AMPG) for all vehicles operated. This AMPG is then divided into the total miles traveled within South Dakota by all vehicles to determine the total gallons of fuel attributable to South Dakota operations. The gallons thus calculated shall be multiplied times the special fuel per gallon tax rate currently in force at the time the return is completed to determine the total tax due from the licensee. This tax liability can be credited in the amount of any South Dakota special fuel tax paid at the time the fuel is purchased within this state. Over purchases of special fuel which result in a tax overpayment shall be refunded to the licensee in accordance with the provisions of § 10-47B-177.