Abstract: Shengtuo Oilfield of Dongying Depression is ternary mixed oil derived from the multiple source rocks and multistage accumulation. The early-accumulated oil was from the upper Es₄, and it suffered biodegradation in the tectonic movement. The late-accumulated oil was from the lower Es₃ and the upper Es₄. Absolute quantitative analyses of biomarkers in the selected three typical end-members show that the average contribution of source rock in the upper Es₄ is 39% in the early accumulation, and the contribution rates of source rocks in the upper Es₄ and the lower Es₃ during the late accumulation are respectively 30% and 31% in the Es₂ reservoirs in Tuo 2 Block. In the Es₂ reservoirs of Tuo 3 Block, the contribution rate of the mixed oils in the upper Es₄ source rock is 41% in the early accumulation, and the contribution rates of source rocks in the upper Es₄ and the lower Es₃ in the late accumulation are about 33% and 26%, respectively. The contribution of the lower Es₃ source rock is reduced from Tuo 2 Block to Tuo 3 Block. The contribution rate of source rock in the upper Es₄ to the Es1 reservoir of Tuo 2 Block is 8% in the early accumulation and 24% in the late accumulation, the contribution rate of the lower Es₃ source rock is 68%. The mixing ratio of oils in this block differs from that in the main oil-bearing layers.