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
Natural-gas processing of three types of wells: crude oil wells, gas wells, and condensate wells. Natural gas that comes from crude oil wells is typically called "associated gas". This gas can have existed as a gas cap above the crude oil in the underground formation, or could have been dissolved in the crude oil. Natural gas from gas wells and from condensate wells, in which there is little or no crude oil, is called "non-associated gas". Gas wells typically produce only raw natural gas, while condensate wells produce raw natural gas along with other low molecular weight hydrocarbons. Those that are liquid