Based on the geological background and Gammacerane/C31H(S+R)ratios,source rock depositional environments of the studied oil samples(194)from 13 oilfields were classified into three groups according to salinity:saline-lacustrine facies,fresh to brackish lacustrine facies(including linmetic facies),and semi-saline to saline facies(including marine facies of the Tarim Basin).C5-C13 compound groups in the crude oils were separated by GC,and about 286 compounds were qualitatively analyzed.The geochemical application of the C6-C13 compound groups and their ratios between each group with individual carbon number was investigated.Our studies show that(1)C6-C13 compound groups and their ratios in the crude oils could serve as new reliable parameters for oil-oil correlation because the C6-C13 light fractions are the major oil component,especially in light oil or condensate,in which they account for almost 90%of the whole oil;(2)the compound groups of C7 light hydrocarbons in oils derived from different depositional environments with different salinity have different characteristics;(3)C6-C13 compound groups and ratios may be affected by other factors such as maturity,but they are mainly controlled by salinity of depositional waters.