Natural gas is often referred to a gas mixture dominated by hydrocarbon, which is preserved in subsurface reservoirs, including oilfield gas, gas field gas, coal bed methane, mud volcano gas and biogenic gas and so on. Natural gas will gradually replaces oil as a top important energy in the energy mix worldwide in the 21st century.

China is one of the largest countries enriched with natural gas resources. Generally, natural gas in the country is distributed in six areas: the eastern, central , western , southern China, Tibet and offshore. As of the end of 1998, 162 gas-fields and 230 gas reservoirs had been discovered in total, including a super giant gas field with a proven OGIP 3097.95×108m3; 16 large gas fields with a proven OGIP 6730.37×108m3 totally; 29 medium gas fields or reservoirs with a proven OGIP 4798.88×108m3 totally and 346 small gas fields or reservoirs with a total proven OGIP 4825.89×108m3 .