Off-Road Diesel Fuel Off-Road Diesel Fuel (as opposed to On-Road Diesel Fuel) is used for vehicles and equipment that do not drive on public roadways. Since this fuel is reserved for off-road use, no road taxes are applied to the purchase of this fuel. Off-Road Diesel fuel is common in construction sites and equipment such as excavators, generators, backhoes, bulldozers, etc. It is also commonly used in farm equipment and various types of factory equipment. Off-Road Diesel Fuel is dyed red to distinguish it from On-Road Diesel fuel. All diesel fuel that we sell is ultra low sulfur diesel fuel at 15ppm. If you would like to learn more about the uses and regulations regarding diesel fuel, please call our offices at 508-668-8200. We look forward to hearing from you. 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.