# Petroleum

**Source:** Buckhead Energy Oil & Gas Encyclopedia (https://www.buckheadenergy.com/learn) — canonical: https://www.buckheadenergy.com/what-is-petroleum

Petroleum is a naturally occurring liquid mixture of hydrocarbons — crude oil, along with the natural gas often found with it — formed from the remains of ancient marine organisms buried in sedimentary rock and transformed by heat and pressure over millions of years.

## How petroleum forms
Petroleum begins as organic matter — mostly microscopic marine life — that settles into sediment and is buried. As layers pile on, rising heat and pressure over geologic time cook that organic material in a "source rock," converting it into hydrocarbons. Those hydrocarbons then migrate upward through porous rock until they are trapped beneath an impermeable layer, forming the reservoirs that wells produce from. Where the conditions were hotter, the result skews toward natural gas; cooler, toward oil.
This is why petroleum is a finite, non-renewable resource: it took millions of years to make, and reservoirs deplete as they are produced.

## What comes out of it
Crude petroleum is a mixture, and refining separates it into products by boiling point — gasoline, diesel, jet fuel, heating oil, lubricants, asphalt, and the petrochemical feedstocks behind plastics and countless consumer goods. The natural gas produced alongside oil is processed separately into pipeline gas and liquids. For a mineral owner, what matters is that your minerals are the source of all of it — and your royalty is a share of the value of that raw petroleum as produced.

## Frequently asked questions

**What is petroleum?**
A naturally occurring mixture of hydrocarbons — crude oil and the natural gas found with it — formed from ancient marine organic matter buried in sedimentary rock and transformed by heat and pressure over millions of years.

**How is petroleum formed?**
Organic matter settles into sediment, is buried, and is cooked by heat and pressure in a source rock over geologic time into hydrocarbons, which migrate and collect in reservoirs trapped beneath impermeable rock. Hotter conditions favor gas; cooler, oil.

**Is petroleum the same as oil?**
Crude oil is the liquid form of petroleum, and "petroleum" is often used to mean crude oil. Strictly, petroleum refers to the whole naturally occurring hydrocarbon mixture, including the natural gas commonly produced with the oil.

## Related terms
- [What is natural gas?](https://www.buckheadenergy.com/natural-gas)
- [Upstream oil & gas](https://www.buckheadenergy.com/upstream-oil-and-gas)
- [Oil & gas royalties](https://www.buckheadenergy.com/oil-and-gas-royalties)

_Educational information only, not legal or tax advice. Buckhead Energy is a direct buyer of oil & gas mineral and royalty interests._