Performance tests at full rack and 1400 rpm using a single cylinder diesel engine were made to determine the effects of three different micronized coal-fuel oil slurries being considered as alternative fuels. Slurries containing 20, 32, and 40 percent by weight micronized raw coal in No. 2 fuel oil were used. Results are presented indicating the changes in the fuel flow rates, concentrations of SOX and NOX in the exhaust, exhaust opacity, power and efficiency, and in wear rates relative to operation on fuel oil No. 2. The engine was operated for 10 hrs. on all fuels except the 40% by weight slurry. This test was discontinued because of extremely poor performance. Results indicate that the coal is largely inert in this situation and will cause a net increase in oil used and very rapid wear.