Performance and fuel consumption of a single-cylinder, direct-injection diesel engine were determined for both an untreated diesel fuel and for the same fuel treated with a platinum-based fuel additive package. The platinum was in an organometallic compound which was soluble and stable in diesel fuel. The fuel additive package was supplied by Fuel Tech, Inc., of Stamford, Connecticut. The engine, a Cooperative Lubrication Research (CLR) engine, was operated for 185 hours on untreated fuel (a low sulfur no. 2 diesel fuel), 236 hours on treated fuel and then 217 hours on the untreated fuel. Engine operating conditions were varied among three steady-state operating conditions at moderate load at 1300, 1600 and 1900 RPM.At the end of the 236 hours in which the additive treated fuel was used, the average brake specific fuel consumption (BSFC) decreased by approximately 9% at 1300 RPM, 5% at 1600 RPM, and negligibly at 1900 RPM. To understand the causes of the BSFC improvements, cylinder pressures were compared for the same conditions. This examination revealed that the cylinder pressures throughout portions of the compression and expansion stroke were higher after the additive was used. The lower BSFC values were attributed to increased indicated work due to shorter ignition delay periods and slightly greater instantaneous heat release rates during portions of the expansion stroke.