Methane gas is also known as landfill gas. It contains about 40 - 60% of methane and the remaining is mostly carbon dioxide. Methane gas may also contain various amounts of oxygen, nitrogen, water vapor, hydrogen sulphide, and other contaminants. The other contaminants can be divided into two types:
Non-Methane organic compounds – they are present in small amounts (less than 1%). They mostly contain various alkanes and other hydrocarbon molecules.
Non-Methane inorganic compounds – they mostly contain mercury. Sometimes radioactive contaminants such as tritium can be found in methane gas.