Biogas is a gaseous fuel, especially methane, produced by the fermentation of organic matter. It is a source of renewable energy that occurs naturally through the process of anaerobic digestion as organic material breaks down in oxygen-free environments such as stomachs, landfills or ponds. It is combusted to generate electricity or provide heating. 

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Biogas is composed primarily of methane, as well as carbon dioxide, and contains trace gasses such as hydrogen sulphide, nitrogen, and oxygen. The relative content of each of these gases is a function of the substrates being digested; as well as digestion conditions. 

Biogas is typically fully saturated when produced, and requires treatment to remove impurities and moisture before use.