Natural Gas Basics

The word "gas" is a confusing term because it is used to describe many different substances that are similar but not exactly the same. For example, the "gas" you put in your car is gasoline, one component of crude oil, or petroleum. Petroleum is a dark, sticky liquid mixture of compounds formed underground by the decay of ancient marine animals.

Natural gas also comes from the decay of ancient organisms, but it naturally takes a gaseous form instead of a liquid form. Natural gas commonly occurs in association with crude oil. It is derived from both land plants and aquatic organic matter and forms above or below oil deposits. It is often dissolved in crude oil at the high pressures existing in a reservoir. There are also reservoirs of natural gas, known as non-associated gas, that contain only gas and no oil.


Natural gas consists primarily of methane and other hydrocarbon gases. Hydrocarbons are organic compounds composed only of the elements carbon and hydrogen. The hydrocarbons in natural gas are called saturated hydrocarbons because they contain hydrogen and carbon bound together by single bonds. As the diagrams show, methane is the simplest saturated hydrocarbon.


Like gasoline, natural gas is combustible, which means it can be used in a combustion engine like gasoline. But cars that could burn natural gas didn't appear on the scene until the 1930s.