California regulations require a maximum of 10% aromatics content in vehicular diesel fuel starting on October 1, 1993. This is in addition to the Federal regulations requiring a maximum 500 ppm sulfur content. Compliance with the low aromatics rule will require major investments in California refineries. Refiners have the potentially less-costly option of producing a higher aromatics diesel fuel if they can demonstrate equivalent emissions relative to a 10% aromatics reference fuel.Chevron U.S.A. Products Company has received the first certification from the California Air Resources Board (CARB) for an alternative diesel fuel. In addition to passing the stringent CARB equivalency test for oxides of nitrogen, particulate matter, and soluble organic fraction, the certified fuel formulation performed better than the reference fuel in reducing total hydrocarbon and carbon monoxide emissions.This paper summarizes the research and development carried out at Chevron Research and Technology Company (CRTC) leading to this fuel formulation and the CARB certification. Fuel properties for the certified fuel, as well as those for the reference fuel are also presented.