This is a review paper on the source of methane in the subsurface and secondary alterations it may be exposed to. Background information on the behaviour of methane, how to determine the source in natural gas, microbial methane versus thermogenic methane. Also info on how it is produced relative to conventional gas recovery, and whether it could be a potential renewable resource. How monitoring for methane might be undertaken and some future research directions are also covered. These components are to fulfil the requirements of the agreement with NSW Chief Scientist and Engineer's office contract.