A number of oil seepages displaying paleoreservoirs have been found in the Mesozoic marine sedimentary formations of Qiangtang Basin. According to correlating the geochemical data achieved with 242 source rock samples from the Jurassic Sowa, Xiali, Buqu, Sewa and Quse Formations and Upper Triassic Xiaochaka Formation, as well as 6 oil seepages samples from the Jurassic Xueshan, Sowa, Xiali and Buqu Formations, including the plots of n-alkane distribution, the relative content of poly-aromatics, the steroid composition,and the relative content of steroid and terpenoid hydrocarbon, etc., it is suggested that the Middle Jurassic Buqu source rock is the contributor to most of the paleoreservoirs so that it is maybe at least one of the mail oil source formations of the paleoreservoirs in the Basin. The paleoreservoir in Upper Jurassic Xueshan Formation is weakly correlative with the 6 sets of source rock formations, which implies that the oil in it is likely to derive from another source rock.