2 minute read • Graham Lumley • Last update November 2023
While the terms crude oil, oil, and petroleum are often used interchangeably, they can be described in slightly different ways. Crude oil refers to the mix of hydrocarbons that are extracted from the earth at oil wells and drilling sites. Petroleum products are what result after crude oil is refined at processing plants into products such as gasoline, jet fuel, or propane. The word “petroleum” on its own refers to both crude oil and the refined petroleum products.
API gravity stands for American Petroleum Institute gravity. This is a measure of how heavy or light a petroleum product is in comparison to water. If an oil’s API gravity is greater than 10, it will float on water. If it is less than 10, it will sink in water.
According to the Environmental Protection Agency (EPA), there are four different classes of crude oil in reference to oil spills and how to go about cleaning up the incident.
Class A oil is fluid, odorous, spreads quickly, and usually flammable. They are likely to be toxic to humans and animals. This class includes products such as jet fuel, kerosene, and gasoline. Class A has an API gravity of 31.1 or higher.
Class B oils are less fluid and are characterized by a waxy texture. They are not as toxic as Class A. Diesel fuel is considered a Class B crude oil. Class B has an API gravity between 22.3 and 31.1.
Class C crude oil is thick, viscous, and tarry or sticky. They are even less toxic than Class A and B, but they adhere more firmly to surfaces and would be harder to clean up in an oil spill. Class C has an API gravity below 22.3.
Class D crude oils are the thickest of the four classes. If wildlife gets caught or smothered they may still perish by drowning or by ingesting the substance. This heavy oil is used to fuel some of the largest marine vessels. Class D crude oil has an API gravity less than 10.
There are over 160 types of crude oil available on the global market, all characterized by the geographic location from which they were extracted from the earth.
The three most valuable types of crude oil are:
