Abstract: Southwest depression in Tarim basin is a complex foreland type as a result of long term evolution. Each movement after Permian,especially Himalayan movement in Cenozoic caused Tianshan and Kunlun mountains successively elevate and overthrust to-ward the basin, thereby resulting in large scale thrust faults and fault-related folds in fore-land depression. Various traps related with the uplift, fold and thrust fault may form dif-ferent reservoir types if there was enough oil and gas supply. Paleozoic traps occur in small amounts in which anticline, fault, lithologic and stratigraphic unconformity reser-voirs are dominant. Meso Cenozoic traps occur in large amounts in which compaction anti-cline, fault-anticline, fault and lithologic reservoirs are dominant. The key to the forma-tion of Paleozoic and Meso-Cenozoic reservoirs is that the source rock is directly or indi-rectly communicated with the reservoir through the fault. Otherwise, it is difficult to dis-cover oil and gas even in the best-quality traps.

Key words: Tarim basin, Southwest, depression, Reservoir forming, Source bed, Trap, Fault