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How do heat and pressure turn kerogen into crude oil 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.

The transformation of kerogen into crude oil and natural gas occurs through a process called thermal degradation, which takes place during the mature stage of hydrocarbon formation.1

As organic-rich sediments are buried deeper, they are subjected to increasing temperatures and pressures. Within a specific environment known as the oil window—typically occurring at depths between 760 and 4,880 metres and temperatures of 65 °C to 150 °C—the heat causes the cracking of complex kerogen molecules. This thermal energy breaks the chemical bonds of the kerogen, releasing attached paraffin chains and producing various soluble bitumen compounds, which eventually evolve into the diverse hydrocarbons found in crude oil.12

Pressure from overlying sediments also plays a critical role by initiating primary migration, which helps expel these newly generated hydrocarbons from the source rock. If temperatures continue to rise beyond the oil window, the kerogen becomes more stable, and the primary product shifts from liquid oil to dry thermal methane gas.21