Methane is a chemical compound with the molecular formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning one molecule of methane in the presence of oxygen releases one molecule of (carbon dioxide) and two molecules of : Methane's relative abundance and clean burning process makes it a very attractive fuel. However, because it is a gas (at normal temperature and pressure; see STP), methane is difficult to transport from its source. In its natural gas form, it is generally transported in bulk by pipe or LNG carriers; few countries still transport it by truck. One of these countries is the USA.

Methane is a relatively potent greenhouse gas with a high global warming potential (i.e., warming effect compared to carbon dioxide). The Third assessment report of the IPCC stated that when averaged over 100 years each kg of warms the Earth 25 times as much as the same mass of . The Fourth assessment report has updated this number to include indirect effects and states that the relative impact of to averaged over 20 years is 72. . The reason for this discrepancy is that methane in the atmosphere is eventually oxidized, producing carbon dioxide and water. As a result, methane in the atmosphere has a half life of seven years (every seven years, the amount of methane halves).

The abundance of methane in the Earth's atmosphere in 1998 was 1745 parts per billion, up from 700 ppb in 1750. In the same time period, CO 2 increased from 278 to 365 parts per million. The radiative forcing effect due to this increase in methane abundance is about one-third of that of the CO 2 increasehttp://www.grida.no/climate/ipcc_tar/wg1/221.htm. In addition, there is a large, but unknown, amount of methane in methane clathrates in the ocean floors. Global warming could release this methane, which could cause a further sharp rise in global temperatures. Such releases of methane may have been a major factor in previous major extinction events. The Earth's crust also contains huge amounts of methane. Large amounts of methane are produced anaerobically by methanogenesis. Other sources include mud volcanoes which are connected with deep geological faults.