Abstract: The Z12-G oilfield in the Pearl River Mouth Basin is an important oil discovery in the Paleogene Enping Formation in the eastern South China Sea in recent years, which has greatly improved the confidence of new depression and the Paleogene oil exploration in shallow water areas. The uplift structure Z12 is adjacent to the two subsags: the Northwestern Subsag and Western Subsag of the Lufeng 13 Sag. Conventional oil source correlation cannot determine the oil source of the reservoir. The unknown oil source relationship and unconfirmed hydrocarbon source rock development restrict the understanding of the exploration potential of new depressions in the area with few wells. To reveal the origin of oils, a detailed biomarker analysis of crude oil and source rock was carried out, especially the systematic semi-quantitative tracing of crude oil migration and experimental analysis of carbon isotope of saturated hydrocarbon monomer hydrocarbon. In addition, oil and gas migration simulation, fault activity rate, and seismic relative ratio analysis were combined for oil source tracing. Results indicate that oil from Z12 oilfield is generated from semi-deep to deep lake facies, which not only has the characteristics of double-sag contribution from the Northwestern Lufeng 13 Subsag and the Western Lufeng 13 Subsag source rocks, but also has the characteristics of short-distance near-source charging in the northwest sag. It is confirmed that the development of semi-deep to deep lacustrine source rocks in the Northwestern Lufeng 13 Subsag and their contribution to the accumulation of reservoirs in the sag uplift. The results provide a solid foundation for the exploration of targets around the Northwestern Lufeng 13 Subsag.