Sixty-eight species of fossil spores and pollen referred to 31 genera extracted from the crude oil samples which were collected from the Neogene reservoirs of the Qaidam Basin in Qinghai Province were recorded. Based on the investigation of the spores and pollen in crude oils and the comparison with those in potential source rocks, the petroleum source rocks of the petroliferous region were determined. On the basis of the paleoecological characteristics reflected by the original plants producing the spores and pollen, the sedimentary environment of the petroleum source rocks was discussed. The fossil spores and pollen found from the crude oils of the Neogene reservoirs of the Qaidam Basin comprised mainly Deltoidospora regularis, Lygodiumsporites pseudomaximus, Polypodiaceaesporites haardti, Polypodiisporites favus, Echinosporis qaidamensis, Podocarpidites paranageiaformis, P. verrucorpus, P. qigequanensis, Abiespollenites lenghuensis, Abietineaepollenites cembraeformis, A. lenghuensis, Pinuspollenites labdacus, P. banksianaeformis, P. mangnaiensis, Piceaepollenites alatus, P. tobolicus, P. planoides, Cedripites deodariformis, C. pachydermus, C. ovatus, C. microsaccoides, Keteleeriaepollenites mangnaiensis, K. megasaccus, Tsugaepollenites igniculus, T. viridifluminipites, T. spinulosus, Ephedripites fusiformis, E. fushunensis, E. ganchaigouensis, E. mangnaiensis, Salixipollenites elegans, Betudaepollenites lenghuensis, Momipites coryloides, Quercoidites henrici, Q. microhenrici, Cupuliferoipollenites fusus, Mediaceoidites rhomboiporus, Chenopodipollis multiplex, C. microporatus, Nitrariadites pachypolarus, Tubulifloridites macroechinatus, T. minispinulosus and Artemisiaepollenites sellularis. The results of this study indicated that the Oligocene to Lower Miocene Ganchaigou Formation and the Upper Miocene to Lower Pliocene Youshashan Formation should be the petroleum source rock series of the petroliferous region; the petroleum source rocks might have been evolved in the lacustrine sedimentary environment under warm and semi-wet to semi-arid climatic conditions.
