Engine hardware modifications, fuel and lube oil properties, electronic controls, and aftertreatment devices may all play a role in meeting future heavy-duty diesel engine emission standards. Detroit Diesel Corporation (DDC) is actively involved in evaluating the contributions of these technologies to reduce emissions as well as evaluating the impact on initial and life cycle system cost, fuel consumption, reliability and durability. This paper focuses on the potential of low emission diesel fuels to contribute to lower engine-out emissions.DDC has been testing low emission diesel fuels with low sulfur and aromatics and higher cetane number, synthetic diesel fuels, and today's fuels with various additives. Other industry programs have generated similar data. These results have led us to the conclusion that a significant contribution can be made by tailoring future diesel fuels to produce low emissions. While more work needs to be done to identify what a low emission diesel fuel specification should be, this paper is intended to stimulate more interest in this subject and encourage engine manufacturers and fuel suppliers to work together to define an acceptable future fuel.