The West Siberian Basin is a Mesozoic - Cenozoic giant rift basin rich in oil and gas with an area over 238×104 km2. The high-quality source rocks and reservoirs of the basin are developed in the post rift depression stage of Jurassic - Cretaceous, which is obviously different from the characteristics of typical rift basins where oil and gas are concentrated in rift strata. Based on the systematic lithofacies paleogeographic mapping, analysis of elements and assemblages of reservoir forming, this paper divides the reservoir forming assemblages developed in the basin depression stage, discusses the oil and gas distribution law of each reservoir forming assemblages, and points out the exploration direction that needs to be focused on in the future. The results show that the West Siberian Basin goes through a longtime, large-scale transgression-regression sedimentary cycle from the Early Jurassic to the Early Cretaceous Barremian, which controls the development of the major source rock and the lower reservoir forming assemblages within the basin. During the late Barremian to the end of the Late Cretaceous, the basin changes into the short-period and multiple transgression-regression sedimentary cycles, which control the development of the upper reservoir forming assemblages. The Jurassic-Cretaceous can be vertically divided into seven reservoir forming assemblages. Most of the oil and gas are enriched in the reservoir forming assemblages of the Lower Cretaceous Berriasian to Barremian and upper Aptian to the Upper Cretaceous Cenomanian. The large structural traps of the Pourskoye Formation of the upper Aptian to Cenomanian assemblages in the northern shelf and the lithological traps of the Tyumen Formation and Vasyugan Formation of the Upper Jurassic assemblages in the southern land will be the two most important favorable exploration fields in the future.