Biodiesel is fuel derived from used cooking oil and other sources for use in diesel engines. If waste oil is simply discarded it pollutes the environment, and so recycling it can kill two birds with one stone. Compared with diesel oil made from petroleum, black soot is reduced to less than one-third in biodiesel, and there are almost no emissions of CO2 and sulfur oxides. In Japan, 100% biodiesel vehicles are excluded from the diesel oil delivery tax.