Abstract: The geological survey of field outcrops and the comprehensive analyses of rock samples and the data from drilling and seismic show that the dark mudstone and limestone of Carboniferous and Ordovician in eastern Qaidam basin are medium- good hydrocarbon source rocks. In the northern margin of Qiadam basin, some petroleum has been found in Mabei, Nanbaxian and Yuka areas; in the western margin of this basin, oily bitumen are filled in pores of Ordovician limestone in Heishuigou area; and in red sandstone core from Upper Jurassic in Huocan-1 Well, light crude oil seepage is found probably from Carboniferous source rocks. These data indicate that Qaidam basin had the courses of petroleum generation, migration and accumulation in Paleozoic, so possessing the basic conditions of oilgas generation and the good prospects for oil-gas exploration in Qaidam basin.

Key words: Qaidam basin, Palaeozic, source rock, oil seepage, exploration prospect