American Petroleum Institute gravity scale
Quick Summary
The American Petroleum Institute (API) gravity scale is a measure of a liquid's density relative to water, with higher API gravity values indicating lower-density liquids. Pure water is assigned an API gravity of 10°. Liquids lighter than water, such as crude oil, have API gravities greater than 10°.
Crude oils are classified based on their API gravity:
* Extra heavy: Below 10° API
* Heavy: 10°–20° API
* Medium: 20°–25° API
* Light: Above 25° API
This classification is important because it helps categorize crude oils by their mobility and ease of recovery, influencing their value and how they are processed in refineries. Crude oil itself is a complex mixture of hydrocarbons, varying in composition and physical properties like viscosity and color.123
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