In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons.[1] Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including deep water marine, lacustrine and deltaic. Oil shale can be regarded as an organic-rich but immature source rock from which little or no oil has been generated and expelled.[2] Subsurface source rock mapping methodologies make it possible to identify likely zones of petroleum occurrence in sedimentary basins as well as shale gas plays.