Abstract: Upper Ganchaigou formation of Neogene is the major source rocks in western Qaidam basin.Its geochemical feature is studied on the basis of previously studied results.The organic carbon content of 0.3% cut-off value is determined, by which the hydrocarbon generating efficiency of 1.23% is offered, being obviously lower than 11.5% of Jurassic formation of Cook Gulf area in Alaska of America given by Leslic B.Magoon in 1994.The study shows that the hydrocarbon may be accumulated in the non-structural traps to be found.These traps should consequently be the important targets for further exploration in the studied area.

Key words: Qaidam basin, Neogene, source rock, petroleum accumulation, efficiency