Encyclopedia Article


Petroleum occurs naturally near the earth's surface in liquid, gas, and solid forms. The word petroleum in Greek literally means rock oil. Petroluem is a naturally-occurring energy sources known as a fossil fuel, meaning it derives from previously living carbon-based organic lifeforms that have been transformed, via a variety of chemical processes over time, into carbon-based inorganic substances from which humans have learned to extract stored energy.

Photo Credit: 

"Recirculating petroleum from the McClintock Well #1, the oldest continuously producing oil well, July 30, 2011" by Niagara is licensed under CC BY-SA.