The primary element of biogas is the same as for Natural gas namely methane (CH₄), the main difference being that the Natural gas is a fossile fuel while the biogas normally is generated from contemporary renewable sources.

Biogas is generated from decay of organic material without oxygen. This process occurs in landfills. One can also produce biogas from food waste, manure and sewage sludge. In theory, all material of biological origin may be used as raw material.

Engines or machinery suited for natural gas may also be fueled by biogas.

The exact composition of biogas will vary with the actual raw material, the generation process and the decomposition process. The main components of biogas are: methane (CH₄), 60 – 70 %, carbon dioxide (CO₂), 30 – 40 %, hydrogen sulfide (H₂S) 50 – 2000 ppm.