Crude oil is not a uniform liquid but rather a range of liquids with differing amounts of hydrocarbons. It is divided into grades ranging from light, which has a density of around 790 kg/m3, to extra heavy, which has a density of around 970 kg/m3.
While the density of crude oil can be expressed in common scientific units, it is more often expressed in a measurement called API gravity. This is a measurement of how heavy a crude oil is compared to water. If its API gravity is larger than 10, it is lighter and will float on water, while if less than 10, it is heavier and sinks. In this measurement, light crude oil has an density of greater than 31.1° API, while extra heavy crude oil is below 10° API.