Abstract: The organic carbon and hydrocarbon potential have long been considered as two most important organic geochemical signatures in the assessment of the source rocks in sedimentary basins.The routine techniques for the recovery of organic matter abundance in the assessment of high-maturity and supermature source rocks include pyrolysis simulation and thermal-pressure simulation,which are not precise enough to be used alone or too expensive to be suitable for the popularization.In this paper,a new method is introduced to estimate original organic carbon in the marine argillaceous source rocks according to Mo-TOC correlation exemplified by the Cretaceous marine mudstones and shales in southern Xizang.If this method is viable,it will contribute a lot to the assessment and prediction of oil and gas resources in the high-maturty and overmature source rocks in China.