Abstract: Oils from well Qun-5 and well Qu-1 in the Tarim Basin contain abundant fatty acids and a series of long-chain alkyl cyclohexanes.The compositions of fatty acids are in the range of C₁₀-C₂₆,and exhibit a model distribution with maximum at C₁₆ for oil from well Qun-5 and at C 15 for oil from well Qu-1.Studied data show that these fatty acids come mainly from their source rocks and are derived from algae and bacteria.The compositions of long-chain alkyl cyclohexanes are in the range of C₁₂-C₃₂.They contain a model distribution with maximum at C₁₃ for oil from well Qun-5 and bimodel distributions with maxima at C₁₄,C₁₅ or C₁₉.Significant differences in the distributions of fatty acids and long-chain alkyl cyclohexanes in oils from well Qun-5 and well Qu-1 indicatethat these oils have different oil sources.Together with the features of compositions of carbon isotopes,long-chain tricyclic terpanes,hopanes and steranes,it is suggested that oil from well Qun-5 originate from Cambrian-Ordovician marine carbonate source rock and oil from well Qu-1 originate from Carboniferous marine mudstone source rock.