In the United States and Canada, the state and provincial taxes on most motor fuel consumed by heavy trucks engaged in interstate commerce are levied on the basis of the estimated fuel consumption in the state or province and that jurisdiction's motor fuel tax rates. This is achieved by apportioning the consumption of motor fuel by "qualified motor vehicles" among the states and provinces on the basis of the mileage travelled in each jurisdiction. As traditionally implemented, this system entails substantial costs of compliance and administration since it is necessary to keep track of both the distance driven and the fuel purchased in each jurisdiction. Enactment of the International Fuel Tax Agreement has substantially reduced these costs, but they remain significant. This article describes the approach to the taxation of commercial motor fuel taken in the US and Canada and provides appraisals of that system from the perspectives of both the trucking industry and taxing jurisdictions.