oil window

The "oil window" is a specific geologic environment where hydrocarbon formation occurs. It is defined by a range of temperatures and depths, typically between 65°C and 150°C (150°F to 300°F) and at depths of about 760 to 4,880 meters (2,500 to 16,000 feet). Within this "oil window," organic matter in source rocks, primarily kerogen, undergoes thermal degradation and cracking, breaking down into lighter hydrocarbon molecules that form crude oil.1

Below this temperature and depth range, crude oil is no longer stable, and the primary hydrocarbon product becomes dry methane gas. Conversely, above the oil window, kerogen becomes chemically stable, and significant hydrocarbon generation ceases. The geothermal gradient of a region influences the depth at which the oil window exists; higher gradients mean shallower depths but a narrower window.1