Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane. It is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the Earth over millions of years. The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in the gas.

Natural gas is a fossil fuel used as a source of energy for heating, cooking, and electricity generation. It is also used as a transportation fuel and as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals.

Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs and in coal beds. In petroleum production gas is often burnt as flare gas. The World Bank estimates that over 150 cubic kilometers of natural gas are flared or vented annually.

Natural gas is often informally referred to simply as "gas", especially when compared to other energy sources such as oil or coal. However, it is not to be confused with gasoline, especially in North America, where the term gasoline is often shortened in colloquial usage to gas.

The world's largest producers of Natural Gas are Russia, Qatar and the USA with large numbers of commercial hydraulic fracking plays from shale deposits.

Natural Gas is often quoted in terms of 1 million British thermal units or BTU. A BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

There has been a strong pivot emanating from the USA to shift towards Natural Gas due to its comparative cleanliness compared to other fossil fuels. In 2016 US power plants used more Natural Gas than Coal for the first time. Even though Natural Gas burns twice as clean as Coal (releases half as much CO2), Natural Gas’s biggest chemical component is Methane, the worst greenhouse gas of all, and is produced throughout every stage of the Natural Gas cycle, from fracking, distribution and combustion. Because of this Natural Gas also overtook Coal in 2016 in becoming the largest source of emissions in the USA.