Results of an automotive technology assessment study are presented to provide a basis of comparison for vehicles with alternative power systems. Factors considered include fuel economy, exhaust emissions, multifuel capability, advanced materials, and cost/manufacturability for both conventional and advanced alternative power systems.To insure valid comparisons of vehicles with alternative power systems, the concept of an Otto-Engine-Equivalent (OEE) vehicle is utilized. Each engine type is sized to provide equivalent vehicle performance. Fuel economy projections are made for each engine type considering both the legislated emissions standards (0.4 g/mi HC, 3.4 g/mi CO, 1.0 g/mi NOx) and possible future emissions requirements (0.4 g/mi NOx). The sensitivities of the fuel economy projections to factors such as engine torque boundary, rear axle ratio, performance criteria, and engine transient response are discussed.Using the OEE vehicle concept, projected fuel economies of both small and full-sized vehicles with Stirling engines are up to 40 percent better than baseline vehicles with conventional engines. Vehicles with Brayton engines show up to a 30 percent better fuel economy than the baseline in full-sized vehicles, but offer little fuel economy advantage in small vehicles. Advanced continuous combustion power systems (Brayton and Stirling) offer advantages over the baseline vehicles in the areas of exhaust emissions and multifuel capability; however, their initial costs are projected to be substantially higher.