Abstract: There are five suites of source rocks in the western part of the Tarimu Basin, the Jurassic being a suite of practical value, with abundant organic materials of very good properties and with appropriate maturity. The Cretaceous-Lower Tertiary series is very prospective, though the conditions for oil generation along the basin margin are not so favourable. It is a marine deposit controlled by faults. Source rocks of considerable thickness are supposed to exist in the Kashi-Yecheng and Awati-Luntai depressions. Crude oils are classified into four types according to their properties. The oils from North Bancheng and Wuqia are characteristic of continental origin, with spectra of isoprenoids similar to those for the Jurassic source rocks. They are originated from the Jurassic source rocks. The oils from Kuche and South Yecheng have a low pristane/phytane ratio, their vanandium/nickel ratio is greater than 1; and with the discovery of two pieces of algae fossil, they are identified to be of marine origin. The carbon isotopes from the crude are quite like those in the Cretaceous-Lower Tertiary source rocks, so they are most probably from the Cretaceous-Lower Tertiary source rocks.