Crude oil is a natural, viscous liquid often found in underground reservoirs. It is made up of a mixture of hydrocarbons — compounds that impart the liquid's extreme volatility and flammability. Crude oil is formed by the remains of animals and plants that died millions of years ago combined with layers of sediment. High pressure and heat across millennia have converted those materials into the liquid form of oil found in the ground.

 

Crude oil is typically extracted from the ground by drilling and then sent to refineries. There, it is separated and refined into a wide variety of nonrenewable fuels and other petroleum products. One such fuel is liquid gasoline, or "gas," which often contains other additives, such as corrosion and preignition inhibitors. Like oil, gasoline retains its hydrocarbons and is extremely flammable and volatile. It is used as fuel in internal combustion engines and as a solvent.

 

Since the advent of the automobile, oil products have become the gold standard for engine fuel and are highly coveted commodities as a result. Oil and gasoline also cause a slew of problems for the environment, such as oil spills, air pollution and climate change. (Photo: Shutterstock)