Experimental investigations were made to evaluate the potential of using low-proof ethanol to supplement diesel fuel in agricultural engines. Fumigation, mechanical emulsification, and chemical emulsifiers were used to introduce a significant amount of alcohol with diesel fuel for engine operation. A total of five diesel tractor engines were tested using each of the fuel systems. Exhaust products and fuel usage were determined at various engine speed/load conditions. A 500-hour engine durability test was conducted on three of the engines using 25% 160-proof ethanol with diesel fuel. Two tests were conducted using fumigation, and one test was done with a mechanical fuel emulsifier. Results suggest that approximately 25% alcohol can be used with diesel fuel to realize essentially the same thermal efficiency as diesel fuel. In addition, no adverse effects on engine life expectancy were apparent using 25% 160-proof ethanol fumigated into an engine. However, using the same fuels and a mechanical emulsification fuel introduction system led to premature engine failure.