Natural gas before the natural gas can be transported. Natural gas extracted from oil wells is called casinghead gas (whether or not truly produced up the annulus and through a casinghead outlet) or associated gas. The natural gas industry is extracting an increasing quantity of gas from challenging resource types: sour gas, tight gas, shale gas, and coalbed methane. There is some disagreement on which country has the largest proven gas reserves. Sources that consider that Russia has by far the largest proven reserves include the US CIA (47 600 km³), the US Energy Information Administration (47 800 km³), and OPEC (48
Billion cubic metres of natural gas standard, the gas volume is measured at . That means that 1 billion cubic metres of natural gas by the International Energy Agency standard is equivalent to 1.017 billion cubic metres of natural gas by the Russian standard. Some other organizations use an energy equivalent-based standards. BP uses a standard which is equivalent to per billion cubic metres. Cedigaz uses a standard which is equivalent to per billion cubic metres. Billion cubic metres of natural gas Billion cubic metres of natural gas (abbreviated: bcm) is a measure of natural gas production and trade. Depending of implied standards, this measure may