The thermal level required by a source rock to convert the sedimentary organic matter, mainly kerogen, into petroleum hydrocarbons and finally to gas and refractory carbon during the late stages of maturity. Source rocks have three levels of maturity: early mature source rock, mature source rock, and post-mature source rock. Each stage is based on the extent of heat-driven reactions and the burial depth. The maturity levels are defined by different geochemical measures such as vitrinite reflectance (Ro %), thermal pyrolysis (Tmax), biomarker analysis, and source rock activation energy (Ea).