A review has been made of the current technology of water and alcohol use in automotive diesel engines. Emphasis has been placed on assessing engine test results for seven methods of using alcohols as supplements or complete replacements for petroleum-based diesel fuel. The methods investigated include the dual-fuel techniques of emulsification, blending, fumigation, and dual-injection, and the monofuel techniques of cetane number improvement, spark ignition, and ignition by electrically heated surfaces or glow plugs. With the exceptions of alcohol/diesel fuel blends and heated surface ignition, all methods have been applied to prototype vehicles and proved successful to some extent in field tests of cars, trucks, buses, or tractors. The changes observed, relative to normal diesel fuel use, in power, fuel consumption, thermal efficiency, and exhaust emissions are documented. Other factors evaluated include diesel fuel displacement by alcohol in specific vehicles and projections of potential domestic fuel savings throughout the transportation sector; fuel cost increases; changes in vehicle system hardware, durability, driveability, and safety; and additional study needs.