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 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 represent different value of energy content. According to the standard defined by the International Energy Agency, it corresponds in average to of energy in the case of Russian natural gas and of energy in the case of Qatar's natural gas. According to the standard defined by the International Energy Agency, the gas physical volume is used, which is measured at the temperature of at atmospheric pressure. According to the Russian