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How is crude oil classified based on API gravity?

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The API gravity scale was developed by the American Petroleum Institute to measure the density of oil relative to that of water, with higher values indicating lower-density oils. Liquids lighter than water, such as oil, have API gravities numerically greater than 10. Crude oil is classified as extra heavy (below 10Β° API), heavy (10–20Β° API), medium (20–25Β° API), and light (above 25Β° API).