On the basis of the geochemical indicators such as the oil composition and the litholo— gY and depositional environments of the oil source rocks，this paper mainly discusses the properties of oils and source rocks at different horizons in the Tarim basin．It is pointed out that the composition of biomarkers of oils，relative contents of V and Ni，sulfur content and carbon and hydrogen isotopic compositions can effectively reVeal the nature of oils，the lithology and depositional environment of the source rocks，and their thermal maturity．A number．of qualitative and quantitatiVe indices given in this paper will be conducive to the correlation of oils and source rocks in petroleum exploration．