Biogas is a well-established fuel for cooking and lighting in a number of countries. It is a gas mixture comprising around 60% methane and 40% carbon dioxide that is formed when organic materials, such as dung or vegetable matter are broken down by microbiological activity in the absence of air, at slightly elevated temperatures (most effective between 30 - 40°C or 50 - 60°C). This is the same process as that which occurs naturally at the bottom of ponds and marshes and gives rise to marsh gas or methane.