Natural gas can be "associated" (found in oil fields), or "non-associated" (isolated in natural gas fields), and is also found in coal beds (as coalbed methane). It sometimes contains a significant amount of ethane, propane, butane, and pentane—heavier hydrocarbons removed for commercial use prior to the methane being sold as a consumer fuel or chemical plant feedstock. Non-hydrocarbons such as carbon dioxide, nitrogen, helium (rarely), and hydrogen sulfide must also be removed before the natural gas can be transported.
Natural gas can be "associated" (found in oil fields) or "non-associated" (isolated in natural gas fields) and is also found in coal beds (as coalbed methane) It sometimes contains a significant amount of ethane propane butane and pentane—heavier hydrocarbons removed for commercial use prior to the methane being sold as a consumer fuel or chemical plant feedstock Non-hydrocarbons such as carbon dioxide nitrogen helium (rarely) and hydrogen sulfide must also be removed before the natural gas can be transported