Crude oil is petroleum that has not yet been refined. Sweet crude is oil that has a low sulfur content (less than 0.5% sulfur; any more than this and it is classified as sour crude oil). As removing sulfur requires extra processing, sweet crude is desirable. Light crude oil is petroleum with a low viscosity, flowing freely at room temperature. This oil is considered higher quality because it produces a higher percentage of gasoline and diesel fuel when refined. Thus, light sweet crude oil is the most desirable form of crude oil.