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Why does petroleum move upward through porous rock underground?

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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 moves upward through porous rock primarily due to differences in density between hydrocarbon fluids and the water present in subsurface formations.12

Because nearly all pores in sedimentary rocks are saturated with water, petroleum migrates within an aqueous environment. Since the specific gravity of this formation water is significantly higher than that of oil and natural gas, the hydrocarbons are buoyant. Over geologic time, these lighter fluids float upward through the interconnected pores of permeable reservoir rocks, such as sandstones or carbonates, until they are trapped by nonporous barriers or reach the surface as seeps.132

This secondary migration can occur independently or be facilitated by active water movement, displacement, or diffusion. Additionally, geological processes such as plate tectonics and rock folding can influence the movement of these fluids through the subsurface.1