Abstract: The systematic investigation of the relevant literature on low-grade reserves at home and abroad is made, and the definition and classification of the "low-grade" reserves in Junggar basin are conducted accordingly. Study shows that the low-grade reserves play a significant role in petroleum exploration and development in China. In terms of this definition, it is estimated that the low-grade reserves in Xinjiang Oilfield Company account for 66.99% of the total proven reserves by the end of 2005, of which the produced "high-grade" thin oil reserves that turned into the low-grade reserves due to water cut increase or production rate decline account for 8.8%. Such highgrade reserves are mainly distributed in Triassic and Permian systems of Karamay, Luliang, Cainan and Hongshanzui oilfields. In addition, the major areas for further searching for the "high-grade" reserves could locate the hinterland and southern margin of Junggar basin.

Key words: Junggar basin, oil resource, classification, economic evaluation