Abstract: The West Lishui Sag is located in the north of the Taibei Depression,the East China Sea Basin.Its source rocks and rese rvoir rocks are dark shales and sandstones in the Mingyuefeng Formation(E₁m)and the Lingfeng Formation(E₁l)of the Lower Tertiary.The sag was believed as an oil and gas domain by petroleum geologists.A deeper petroleum system(E₁y-E₁l)and a shallow complex petroleum system(E₁m-E₁w)were identified in the West Lishui Sag.The relationship between source rocks and hydrocarbon accumulation was discussed,and a model of hydrocarbon migration wa s postulated.The petroleum distribution in this sag was clearly defined and po tential targets for prtroleum exploration were pointed out.So that this study w as applicable to hydrocarbon exploration in the Easy China Sea Basin.