Petroleum reservoir

A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence of high heat and pressure in the Earth's crust. Reservoirs are broadly classified as conventional and unconventional reservoirs.

Extends: [Petroleum geology](https://wikipedia.org.ai/Petroleum geology), [Reservoir rock formations](https://wikipedia.org.ai/Reservoir rock formations)