What is the main component of biogas?

Biogas is a mixture of gases containing predominantly methane produced by microbial activity and which may be used as fuel.The type of the gas produced depends upon the microbes and the organic substrates they utilise. In the examples cited in relation to fermentation of dough, cheese making and production of beverages, the main gas produced was CO₂.. However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO₂ and H₂ .