Methane and carbon dioxide make up 90 to 98% of landfill gas. The remaining 2 to 10% includes nitrogen, oxygen, ammonia, sulfides, hydrogen and various other gases. Landfill gases are produced when bacteria break down organic waste. Though production of these gases generally reaches a peak in five to seven years, a landfill can continue to produce gases for more than 50 years. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.