Asphalt and road oil are used primarily by the construction industry for roofing and waterproofing and for road construction. Asphalt is a byproduct of petroleum refining. During the distillation process of crude oil, asphalt does not boil off and is left as a heavy residue. Generally around 90% of crude is turned into high margin products such as gasoline, diesel, jet fuel, and petrochemicals while the other 10% is converted into asphalt and other low margin products. Petroleum refiners sell asphalt to asphalt product manufacturers who produce retail products such as asphalt paving mixtures and blocks; asphalt emulsions; prepared asphalt and tar roofing and siding products; and roofing asphalts and pitches, coating, and cement.