S15 (ULSD) is defined by the U.S. Environmental Protection Agency (EPA) as U.S. diesel fuel with a sulfur content not to exceed 15 ppm (parts per million). S15, S500, and S5000 are designations for diesel fuels that meet 15 ppm, 500 ppm, and 5,000 ppm maximum sulfur content, respectively, as defined in the American Society for Testing and Materials (ASTM) standard D975 Table 1. In different regions of the world ULSD may refer to different maximum sulfur content values, but ULSD and S15 are often used interchangeably in North America (U.S. and Canada).The S15, S500, and S5000 designations also apply to the Canadian diesel market.
For additional information on the new S15 (ULSD) regulations visit the
Clean Diesel Fuel Alliance Information Center