Natural gas

Highly compressible, highly expansible mixture of hydrocarbons with low specific gravity and occurring naturally in gaseous form. Besides hydrocarbon gases, natural gas may contain appreciable quantities of nitrogen, helium, carbon dioxide, hydrogen sulfide, and water vapor. Although gaseous at normal temperatures and pressures, gases making up the mixture that is natural gas vary in form and may be found either as gases or as liquids under suitable conditions of temperature and pressure.