Petroleum, or crude oil, is a naturally occurring liquid recovered from beneath the Earth’s surface. Refining crude oil leads to products like gasoline, diesel fuel or lubricating oils.
Petroleum products are complex mixtures of various hydrocarbons, characterized through their physical properties such as density. The API (American Petroleum Institute) gravity is an alternative value for comparing the densities of different petroleum products.
API gravity is a measure of the weight of a petroleum liquid compared to water. If the API gravity (at t = 60 °F) is greater than 10, it is lighter and floats on water. If it is less than 10, it is heavier and sinks.