A mixture of generally gaseous hydrocarbons and varying quantities of non-hydrocarbons that exist either in the gaseous phase or in solution with crude oil in natural underground reservoirs. Natural gas consists mainly of methane (80%) and significant proportions of ethane, propane and butane. There will always be some condensate and/or oil associated with the gas. The term is also used to mean treated gas which is supplied to industrial, commercial and domestic users and meeting a specified quality.