Natural gas, often referred to as simply 'gas', is a gaseous fossil fuel consisting primarily of methane. Natural gas is found in oil fields, natural gas fields, and in coal beds (as coalbed methane). Before use as a fuel, natural gas undergoes extensive processing to remove almost all materials other than methane.
Natural gas is a major source of electricity generation, and particularly high efficiencies can be achieved through combining gas turbines with a steam turbine in combined cycle mode. Natural gas burns cleaner than other fossil fuels, producing about 30% less carbon dioxide than oil and about 45% less than coal, per unit of energy released. It is also expected that natural gas reserves will peak around 2030, some 20 years after peak oil production. Compressed natural gas is also used as a cleaner alternative to other automobile fuels such as gasoline (petrol) and diesel. Natural gas is also used domestically for cooking and for central heating.
The major difficulty in the use of natural gas is transportation and storage because of its low density. Pipeline transport is economical, but is impractical across oceans. Liquefied natural gas can be shipped in LNG carriers, however the required liquefaction facilities add to the cost. The practice of flaring gas released in the course of recovering petroleum, so adding to greenhouse gas emissions, is now illegal in many countries.