What conditions create the oil window for hydrocarbon formation?

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

The "oil window" refers to the specific geological environment where kerogen undergoes thermal degradation and cracking to generate petroleum compounds.1

This process occurs under the following conditions:

Depth: Typically between 760 and 4,880 metres (2,500 to 16,000 feet).1
Temperature: Temperatures ranging from 65 °C to 150 °C (150 °F to 300 °F).1
Geologic Factors: The window is influenced by the geothermal gradient; in areas with a higher gradient, the oil window may occur at shallower depths in younger sediments, though it becomes narrower.1

Within this window, the mild heating of organic matter over long periods releases paraffin chains and produces various hydrocarbon compounds that constitute crude oil. Maximum generation generally occurs between 2,000 and 2,900 metres. Beyond these conditions—specifically at depths greater than 4,800 metres—crude oil is no longer stable, and the primary product becomes dry thermal methane gas.1