Studies of several options available for future vehicular transportation powerplants have strongly indicated that it is necessary to optimize the vehicle, its fuel, and the refinery as a total system.It is the purpose of this paper to report the relative miles of transportation that can be obtained from a barrel of crude oil by using different types of engines and fuels.This concept is not new. The energy required to manufacture fuels has always been supplied by using part of the energy in the crude oil. However, the importance of the concept is compounded when one considers that large quantities of gasoline are lost due to processing requirements for producing unleaded gasoline octane numbers while concurrently, automotive emission controls and safety regulations increase gasoline consumption.Both of these effects cause a reduced efficiency in the use of crude oil. The only true measure of the impact on energy usage caused by changes in refinery operations and vehicular modifications is to relate the miles of transportation obtained to the energy available in the crude oil. This concept accounts for both the energy needed for fuel manufacture and the energy needed to propel the vehicle.The options that have been studied are: 1. Use of leaded gasoline in an internal combustion engine. 2. Use of unleaded gasoline. 3. Maximum use of diesel engines. 4. Maximum use of the direct injection stratified charged engine. 5. Maximum use of gas turbine engines. It will be shown that the engine-fuel option chosen will have a substantial impact on the United States domestic economy and balance of payments. Furthermore, the choice of the wrong option could seriously restrict the number of vehicles that could be operated if world-wide crude oil availability should become limited in supply.