A measure of the density of petroleum oils used in the US and related to specific gravity:
The specific gravity and API gravity refer to the weight per unit volume at 15.6ºC (60ºF). Most crude oils range between 20 and 45oAPI.
Geology and Earth Sciences
A measure of the density of petroleum devised by the American Petroleum Institute (API). If the API gravity is less than 10 the petroleum is denser than water and will sink; if it is greater than 10 the petroleum is less dense than water and will float. Although the value is dimensionless, it is expressed in degrees (° API).