API gravity

API gravity is a scale from the American Petroleum Institute that measures how light or heavy a crude oil is relative to water, a higher number meaning a lighter oil.

API gravity, developed by the American Petroleum Institute, is a way of comparing how light or heavy different crude oils are relative to water. A higher reading means a lighter oil, one that yields more valuable, easily refined products such as gasoline and diesel per barrel; a lower reading means a heavier oil that needs more complex refining to produce the same fuels.

Refiners pay attention to API gravity alongside sulfur content because together the two largely determine how much a given crude is worth to a refinery and how it is priced relative to other grades. Light, low-sulfur oils are described as sweet crude; heavier, higher-sulfur oils are sour crude. Benchmarks like WTI are defined partly by a specified API gravity range that qualifies for delivery.