Abstract: The migration of oil and gas in a multiple pay, multiple source rock, structurally complex, and extensively faulted region is very complicated. In such regions, a study of the compositions of carbon and hydrogen isotopes is one of the most effective techniques in the investigation of the direction of migration of oil and gas to determine the origin of the oil and gas in certain pay zones and its relation to the source rocks. Based on a correlation of the compositions of carbon and hydrogen isotopes from different source rocks in certain oil-and gas-bearing regions, this paper gives a conclusion that the oil and gas in reservoir Yan-10, Yian Formation in Baiyanjing Oil Fiell are originated from different source rocks. It is demonstrated that the crude oil is migrated from Yinchang Formation(source rock), while the solution gas is mainly originated from the coal-bearing Permian and Carboniferous Formations through migration. It points out also that the gas in Zhouzhuang Gas Reservoir is a thermal cracking gas originated from Funing Formation rather then biogenic gas originated from reservoir formation itself; and that the coaliferous gas accumulated in the coal bearing Xiangxi Group in Naxi Gas Field, Sichuan Province is petroliferous gas originated from the underneath Jialingjiang Formation rather than the coaliferous gas from the reservoir formation itself.