Clear diesel is a type of traditional fuel that doesn't have any added dyes. It's classified as a fossil diesel or mineral diesel and is most commonly used in road vehicles. Diesel fuel is easier to refine from petroleum than gasoline and contains hydrocarbons. In North America, most diesel fuel consumed is ultra-low sulfur distillate/diesel (ULSD) with a sulfur content of 15 parts per million or less. Diesel fuel is preferred for heavy-duty applications because it has 12% more energy per gallon than gasoline.