Britannica Sources used in this answer

How do temperature and depth affect the formation of oil and natural gas?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

structures of common hydrocarbon compounds — hydrocarbon Structures assumed by hydrogen (H) and carbon (C) molecules in four common hydrocarbon compounds.

The formation of oil and natural gas is primarily driven by the thermal degradation of kerogen within sedimentary source rocks. As organic matter is buried deeper, it experiences increasing temperatures, a process known as the mature stage of hydrocarbon formation.1

This process occurs within a specific range known as the "oil window," typically found at depths between 760 and 4,880 metres (2,500 to 16,000 feet) and temperatures ranging from 65 °C to 150 °C (150 °F to 300 °F). Within this window, thermal cracking breaks down heavy molecules into the various compounds that constitute crude oil.1

The specific products generated depend on these conditions:
* Maximum generation: Occurs between 2,000 and 2,900 metres.1
* Wet gas: Forms at depths greater than 2,900 metres.1
* Dry methane gas: Becomes the primary product below approximately 4,800 metres, where temperatures render crude oil unstable.1

While depth is a factor, the geothermal gradient—the rate at which temperature increases with depth—determines the exact location of these zones. In areas with higher geothermal gradients, these processes can occur at shallower depths.1