Unrefined liquid petroleum. It ranges in gravity from 9 to 55 °API and in color from yellow to black, and it may have a paraffin, asphalt or mixed base. If a crude oil, or crude, contains a sizable amount of sulfur or sulfur compounds, it is called sour crude; if it has little or no sulfur, it is a sweet crude. In addition, crude oils may be referred to as heavy or light according to [[API gravity]], the lighter oils having the higher gravities.