Abstract: With a new understanding of petroleum geologic conditions in the Keshi Depression, southwest Tarim, the authors believe that the middle Jurassic Yangye Formation is the major source rocks in the Meso-Cenozoic systems of the area, the Kezilesu Gr. aeolian sandstones of the Lower Cretaceous could be excellent reservoirs and the overlying Upper Cretaceous and Paleogene systems are well-developed regional multiseals, among which the Artashi Fr. gypsum rocks of Palaeocene would be the best. Therefore the source rock, reservoir and regional seals may vertically and horizontally compose of an oil/gas assemblage in the depression. Based on the above considerations, a breakthrough in oil/gas exploration would be expected in proper structures.