Home > Encyclopedia of Science > Petroleum

• Location of world's supply
• The importance of oil
• The future of oil

Petroleum, also called crude oil, is a thick, flammable, yellow-to-black colored liquid. Petroleum was first found oozing out of rocks on Earth's surface. Hence, its name comes from the Latin words petra, meaning rock, and oleum, meaning oil. Petroleum is a hydrocarbon, an organic compound containing only carbon and hydrogen. It is a mixture of other hydrocarbon compounds such as natural gas, gasoline, kerosene, asphalt, and, probably most important, fuel oil.

Today, most scientists agree that oil was formed from the remains of plants and tiny animals that settled to the bottom of ancient oceans. These remains or sediments were buried by layers of mud and sand. Gradually, over millions of years, the weight of these...