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Why is petroleum considered a fossil fuel along with coal and natural gas?

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Multiple large offshore petroleum oil rigs with cranes and equipment stand in the ocean, connected by walkways above the water. — petroleum Liquid petroleum (crude oil)—which is refined into gasoline, diesel, heating fuels, asphalt, plastics, and other useful chemical compounds—is often extracted from the ground using a series of drills and pumps.

Petroleum is classified as a fossil fuel because it is formed through geologic processes acting upon the remains of ancient organic matter. Like coal and natural gas, petroleum represents a concentration of carbon and hydrogen derived from biological precursors.12

While coal originates primarily from the accumulation of land plants, petroleum and natural gas are largely the products of marine organisms. Over millions of years, these organic materials are buried under layers of sediment. As they are subjected to increasing pressure and temperatures within the Earth's crust—specifically within a range known as the "oil window"—these precursors undergo thermal degradation and chemical transformation into hydrocarbons.23

It is important to clarify that while these fuels are derived from ancient life, they are not technically fossils themselves. Fossils typically consist of preserved hard parts like bones or shells, or impressions in rock, whereas fossil fuels are the chemically altered, energy-rich remnants of organic tissues.1