Hydrogen internal combustion engine vehicles present much of the same promise to reduced carbon dioxide emissions. Proponents envision hydrogen Internal Combustion Engine as a bridging technology from gasoline vehicles to hydrogen internal combustion engine. This paper examines the hydrogen Internal Combustion Engine technology, focusing on relevant aspects such as power, fuel economy, tank size, and the state of the technology. An economic analysis is then performed to examine the potential implications of widespread adoption of hydrogen Internal Combustion Engine vehicles. The case for hydrogen Internal combustion engine depends most on key uncertainties in the evolution of vehicle and production technology, the cost of crude oil, and the valuation of carbon dioxide emission reductions. This analysis indicates that promoting hydrogen internal combustion engine vehicles may be a sensible policy goal, but a more prudent policy would first promote gasoline-electric hybrids.