Glossary Term

API gravity
A measurement convention established by the American Petroleum Institute for expressing the relative density of petroleum liquids to water; the greater the API gravity, the less dense the material. API gravities are close (but not equivalent) to specific gravities measured in the Baumé scale, which is the more conventional method of representing the density of a liquid. API gravity = (141.5/specific gravity @ 60°F) – 131.5; thus, a petroleum liquid with an API gravity of 10.0 @ 60°F has a specific gravity of 1.0 (which is the same as water). Petroleum liquids with API gravities greater than 10 API gravity degrees have densities less than water and will float; those with API gravities less than 10 will sink. The API gravity scale is calibrated such that most petroleum liquids (crude oils as well as distillate fuels) will have API gravities between 10 and 70 API gravity degrees.