Natural gas is made up of methane and light hydrocarbons such as ethane, propane and butane, with the addition of gases such as carbon dioxide and nitrogen. The composition of natural gas varies from one field to another. Natural gas from the Groningen field consists of about 81.3% methane and 3.5% higher hydrocarbons (ethane, propane etc.). It also contains about 15.2% incombustible gases (mainly nitrogen and a little carbon dioxide). Natural gas found in other fields usually contains different quantities of methane and higher hydrocarbons and less nitrogen.