There is abundant Oil and gas in the western sag. According to the statistical analysis of the geological factors of 773 reservoirs discovered, it is considered that there are various reservoir types in the sag, with structural and lithological reservoirs dominating and composite reservoirs developing. The statistics data show that nearly 90% of reservoirs are related to faults. The types of reservoir are significantly controlled by structural belt. There are mainly anticlinal and lithological-structural reservoirs in gentle belt, anticlinal and fault block reservoirs in central anticlinal belt, and lithological reservoirs in steep slope belt. Reservoirs are obviously controlled by sedimentary facies, and mainly distribute in fan delta facies, delta facies and turbidite fan facies. The spatial distribution of oil and gas resources follows “the model of the total oil and gas resources balance”, and shows obvious complementary characteristic on both the plane and the stratigraphic horizon. According to research, the distribution of reservoirs is jointly controlled by hydrocarbon generation sag, faults, abnormal pressure and facies in the western sag. Firstly, the active source rock in Sha 3 Member and Sha 4 Member are well development and the resource quantity is very large. So they form the base of hydrocarbon enrichment and control the distribution of reservoirs in Western Sag; Secondly, oil-bearing sand bodies of each Formation and Member are overlapped and continuous plane distribution, which is favorable to lateral migration; Thirdly, the development of pressure relief faults led by the strike-slipping at the end of Dongying phase, which makes the oil and gas large scale and far-distance vertical migration possible.