The oil in the west part of northern slope in Central Tarim Basin can be classified into two types (Ⅰ

Ⅱ) based on the distribution and composition of sterane and terpane. Type-I oil is characterized by relative tow ratio of tricyclic terpanes to hopanes

pregnanes to regular sterane and rearranged steranes to regular sterane

and by relative high ratio of Ts to Tm

C

28

to C

29

sterane and C

30

hopane to C

31

homohopanes. Type-Ⅱ oil has opposite biomarker characters to the type-I oil. The difference implies that there may be at least two oil sources in the study area The correlation between the oils and source rocks indicates that the oil of type-Ⅰ was derived from the Cambrian carbonate source rock

and the oil of type-Ⅱ was derived from the Middle-Upper Ordovician marl source rock.