Hydrogen offers the prospect of plentiful supplies of clean transportation energy. This paper is a comprehensive review and analysis of hydrogen in efficient passenger vehicles. It addresses hydrogen production and distribution, on-board storage technology, refuelling, vehicle performance and safety, the environmental impacts of hydrogen use, and life-cycle costs. The environmental impact analysis focuses on NO, emissions from vehicles, the environmental impacts of making hydrogen from coal, and the contribution to the Greenhouse effect of CO2 emissions from the use of coal-based hydrogen. The life-cycle cost model compares hydrogen vehicles to similar baseline gasoline vehicles, and includes estimates of the total retail cost of liquid and gaseous hydrogen from coal and solar-powered electrolysis, the cost of fuel storage equipment, the cost of pollution control equipment, maintenance costs, other ownership and operating costs, and the external costs of hydrogen use. While there is considerable uncertaintly about several important parameters, I conclude that under certain plausible (though not necessarily likely) conditions-low hydrogen fuel and vehicle costs, high nonmarket costs of gasoline use, and moderately strong efforts to avoid a Greenhouse warming-hydrogen vehicles could be the socially preferred highway transportation option.