A device to convert a diesel engine to dual fuel (propane/diesel) operation was developed and evaluated. Preliminary experimentation has indicated that as much as 30% of the diesel fuel consumed in diesel engines could be displaced with propane, accompanied by an improvement in fuel efficiency, engine maintenance and an overall reduction in emission levels. Dual fuel operations in both transportation and stationary applications would then project a saving of ca 90,000 barrels of diesel fuel per day by the year 1990. A turbo-charged 250 hp diesel engine was directly coupled to a dynamometer under laboratory conditions, and operated at speeds between 500 and 2500 rpm and at various torque levels. At each rpm/torque point the engine first operated on diesel fuel alone, and then increasing quantities of propane were induced into the air intake until detonation occured. Results indicate that the proportion of propane that can be safely induced into a diesel engine varies considerably with rpm and torque so that a sophisticated metering system would be required to maximize diesel oil displacement by propane. Conversion is not cost effective at 1983 price levels.