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We compare the life cycle inventories of near–term fuel–propulsion technologies. We analyze fossil fuels (conventional and reformulated gasolines, low sulfur diesel, and compressed natural gas (CNG)), ethanol from biomass, and electricity, together with internal combustion engines (port and direct injection, spark and compression ignited) and electric vehicles (battery–powered, hybrid electric, and fuel cell). The fuel economy and emissions of conventional internal combustion engines powered by gasoline continue to improve. Unless emissions of pollutants and greenhouse gases (GHG) are stringently regulated or gasoline prices more than double, gasoline powered internal combustion engines will continue to dominate the light duty fleet. Two appealing alternative fuels are CNG and biomass ethanol. CNG cars have low emissions, including GHG and the fuel is less expensive than gasoline. Biomass ethanol can be renewable and have no net carbon dioxide (CO2) emissions.

We analyze alternative fuel/engine internal combustion engine and electric technology options that will be available over the next two decades for powering a large proportion of the U.S. light duty fleet (cars and light trucks). Lifetime private (vehicle, battery replacement and fuel) and social (externalities associated with pollutant and greenhouse gas emissions) costs for the vehicle options are estimated and compared to those of a baseline gasoline fueled internal combustion engine automobile. Technological advances continue to improve the efficiency and environmental performance of low sulfur reformulated gasoline fueled internal combustion engine automobiles. In our judgment, two fuels which may challenge gasoline for use in internal combustion engines are compressed natural gas and biomass ethanol. Compressed natural gas would lower our dependence on foreign energy supplies, would result in lower greenhouse gas emissions, and is cleaner burning than petroleum fuels.