Abstract: The south area in western Qaidam basin is a main area for petroleum exploration in Qaidam basin, with petroleum resources of 15.35×10⁸ t and proved OOIP of 3.53×10⁸ t, which shows that it is in low identified rate and great potential for prospecting. The reservoirs discovered up to now are still dominated by structural reservoirs. With the increase of the explorative extent and the advancement of explorative technology, lithological reservoir exploration is becoming the major domain for petroleum exploration in this area. The petroleum geologic evaluation suggests that the south area in western Qaidam basin develops clastic lithologic reservoir of Tertiary controlled by fluvial delta system, being of broad domain and bright prospect for petroleum exploration. In recent years, the lithologic exploration achievements in such areas as Hongliuquan $E^1_3$ reservoir, Wunan $N^1_2$ reservoir and Kunbei $E_{1+2}$ reservoir support this mature idea and method for further petroleum exploration here.

Key words: Qaidam basin, south area, lithologic reservoir, explorative idea, explorative method