API Gravity is a fundamental ‘bulk property’ measurement of an oil’s density and is a metric that’s used across many sub-disciplines within the Oil & Gas Industry. An oil’s API Gravity can reflect the source organic matter or thermal maturity. Typically, higher API gravities indicate advanced thermal maturities while lower API gravities may result from secondary alteration or primary migration of oils of lower relative maturity. When using API data, it’s important to remember that it is typically measured and calculated at “surface conditions” as opposed to other fluid property measurements that simulate reservoir or downhole conditions.