API gravity

Lower 48 U.S. states production of crude oil by API gravity in January 2015 through July 2019 (48880018261)

API gravity is a measure of how heavy or light a petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. API gravity is used by the petroleum industry to classify oils as light, medium, heavy, or extra heavy. This measurement is important because it affects everything from the pricing of crude oil to its refining process.

Overview

API gravity is calculated using a formula derived by the American Petroleum Institute (API), which gives the measure its name. The formula to calculate API gravity from the specific gravity (SG) is:

API gravity = (141.5 / SG) - 131.5

where SG is the specific gravity of the oil at 60°F (15.6°C) compared to water at the same temperature. The higher the API gravity, the lighter the oil. Light oils generally have an API gravity above 31.1, medium oils are between 22.3 and 31.1, heavy oils are between 10.0 and 22.3, and extra heavy oils have an API gravity below 10.0.

Importance in the Petroleum Industry

API gravity has a significant impact on the petroleum industry's operations and economics. Lighter oils with higher API gravity are usually more desirable because they yield a higher percentage of gasoline and diesel fuel when refined. Consequently, they often command a higher price on the market. Heavy and extra heavy oils require more complex and expensive refining processes to produce valuable fuel products.

Measurement and Classification

The measurement of API gravity is conducted using a device called a hydrometer or through laboratory analysis. The classification of oil into light, medium, heavy, or extra heavy categories based on API gravity helps in assessing its value and determining the most efficient method for its extraction, transportation, and refining.

Environmental and Economic Implications

The API gravity of oil also has environmental implications. Lighter oils tend to produce less sulfur and other pollutants when burned compared to heavier oils. However, the extraction of lighter oils, often found in more accessible locations, can lead to significant environmental disruption. Conversely, heavier oils, such as those extracted from oil sands or through hydraulic fracturing, pose different environmental challenges due to the methods required to extract and process them.

Conclusion

API gravity is a crucial parameter in the petroleum industry, influencing the market value of crude oil, its refining process, and the environmental impact of its extraction and use. Understanding API gravity helps in making informed decisions regarding the exploration, production, and refining of different types of crude oil.

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