API Gravity: API gravity is a specific scale to measure the density of petroleum liquids relative to water. It is calculated using the formula: ( API , gravity = \frac{141.5}{SG} - 131.5 ) where SG is the specific gravity of the oil at 60F (15.6C). API gravity inversely correlates with density: higher API gravity means lower density. Oils with higher API gravity are generally lighter and more valuable because they yield more gasoline and diesel when refined