Abstract: Located in the northeast of China,the Sungliao Basin is a large petroliferous basin of the Meso-Cenozoic era,in which 5,000 meters thick of Cretaceous representing typical continental sediments are deposited.Organic geochemical study reveals that the source materials that form oil in the Cretaceous may be divided into two types: kerogen of humus type from organic matter of terrestrial high plant origin and kerogen of sapropel or transitional type from organic matter of aquatic origin.These two types of source materials come from the semi-deep to deep lacustrine sediments widespread in the basin and afford a rich source for trans formation into hydrocarbons.It brings into our cognizance that the primary source material for oil in the Sungliao Basin is lake organism.The threshold depth for formation of petroleum in the three suites of source rock in the basin lies approximately in the range of 1180～1330 meters.By comparing the organic geochemical index of the source rock with those of the crude oil,it is believed that the oil comes from the nearby source rock.