On-Road Diesel Fuel On-Road Diesel Fuel (as opposed to Off-Road Diesel Fuel) is used for vehicles and equipment that utilize public roadways. This includes anything from personal vehicles to tractor trailers to buses. On-Road Diesel fuel has the appropriate taxes added to the sale for use on the roads. If you are interested in On-Road Diesel fuel delivery, we offer fleet fueling and bulk deliveries. Both options will save your company time and money. All of the diesel fuel that we sell, both on-road and off-road, is ultra low sulfur diesel fuel at 15ppm. WHAT is ULTRA LOW SULFUR DIESEL FUEL (ULSD)? ULSD is diesel fuel with a maximum sulfur content of 15 ppm (parts per million) and is often referred to as S 15. S 15, S500, and S5000 are designations for diesel fuels that meet 15 ppm, 500 ppm, and 5,000 ppm maximum sulfur content, respectively. ULSD will be required for all 2007 and later model year on-road diesel engines.