Natural gas is an important fossil fuel used in electricity generation, kitchen stoves, heating homes and many other residential, commercial, and industrial applications. The cleanest of the fossil fuels, the combustion of natural gas releases fewer pollutants than the combustion of other fossil fuels. Natural gas is also being used as a rich source of hydrogen for fuel cells.

Natural gas that reaches our homes is composed primarily of methane (CH₄). However, upon being extracted from the ground, unrefined natural gas is a mixture of methane (about 70% or more) and other hydrocarbons (about 20% or more) such as ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and pentane (C₅H₁₂) which are collectively known as natural gas liquids.

In addition, unrefined natural gas contains oil, water, carbon dioxide, sulphur and other impurities. For example, the tell-tale rotten egg smell around “sour gas” wells is a result of the higher levels of sulphur, or more accurately hydrogen sulphide (H₂S)(over 5.7mg/m3 of H₂S).

Natural gas can be further processed into a liquid by chilling it to very cold temperatures (-162^oC or -260^oF). This Liquefied Natural Gas (LNG) has a number of advantages, the main one being that a much greater volume of gas can be transported as a liquid than as a gas. In addition, the process of making LNG removes more of the remaining impurities such as sulphur, CO₂, oxygen and water.

Alternative Sources
The primary source of natural gas continues to be natural gas deposits below the earth's surface which are extracted by the oil and gas industry. However, a variety of alternative sources are being explored including the capture of methane as waste gas from landfill sites, and from methane hydrates which are methane hydrocarbons surrounded by a lattice of ice.

Pollution from Natural Gas
The cleanest of the fossil fuels, natural gas still results in the release of CO₂ and nitrogen oxides when burned. In addition, particulate matter, sulphur oxides and reactive hydrocarbons (see VOC) are also produced but in very small amounts compared to the combustion of other fossil fuels.

Where natural gas is also of particular concern is in its contribution to climate change. Methane, CO₂, and water vapour are all important green house gases.