Absolute ethanol can be mixed with No. 1 diesel oil without separation if the mixture remains free of water. Mixtures of diesel oil and up to 30 percent by volume of ethanol were used in laboratory and field experiments in diesel tractor engines. When engines were operated on fuels containing ethanol, the maximum power output of the engines was reduced, fuel consumption increased, engine noise increased, and the delay period was extended. These changes in engine operating characteristics increased in magnitude as the proportion of ethanol in the fuel increased.No significant performance characteristic of the diesel engine measured in this study was improved by the use of a diesel oil-ethanol blend to replace diesel oil to fuel the engine. Based upon this study, there appears to be no valid technical reason to recommend that diesel-powered farm tractors be operated on a mixture of diesel oil and ethanol in preference to diesel oil.