Based on the chromatograms of oils and saturated hydrocarbons,biomarkers and stable carbon isotope analyses,the geochemical characteristics and oil family Classification of crude oils from the Markit Slope in the southwest of the Tarim Basin were investigated.The results showed that crude oils from the Markit Slope are divided into two oil family Classification.Oils collected from the Bashituo oilfield in the western part of the Markit Slope are characterized by high contents of tricyclic terpanes,pregnane,and homopregnane,low contents of garmmacerane (G/H＜0.20),dibenzofuran,and methyl cyclohexane,and light stable carbon isotopic values (the δ13C ValueS of saturated hydrocarbons and aromatic components are less than -34‰ and -32‰,respectively),with the distribution type of steranes being C27＞＞C28＜C29.Condensate oils collected from the Hetian River gasfield in the eastern part of the Markit Slope are characterized by low contents of tricyclic terpanes,pregnane,and homopregnane,high contents of garmmacerane (0.20＜G/H＜0.36),dibenzofuran,and methyl cyclohexane,and relatively heavy carbon isotopic values (δ13C of saturated hydrocarbons and aromatic components (＞ -32‰ and -30.6‰,respectively),with the distribution type of steranes being C27＞C28＜＜C29.In addition,oils from Well Qu 1 have some characteristics similar to those of the above oils,with some special characteristics including high contents of β-carotenes and special distribution of steranes (C27＜C2s ＜C29).