Abstract: Detailed analyses of crude oils and source rock extracts indicate that there are two sets of effective hydrocarbon source rocks in eastern Pearl River Mouth Basin. Typical crude oil derived from the lacustrine source rocks in the Eocene Wenchang Formation is characterized by abundant C304- methylsteranes but relatively little bicadinane chemicals (T), while the typical crude oil derived from Oligocene Enping Formation features in high content of bicadinane chemicals (T) and relatively low content of C30 4-methylsteranes with high Pr/Ph. The chemical compositions of most crude oils coincide with the mixed features of these two source rocks but do not match those unknown source rocks. The comparison of oil sources shows that the crude oils of Xijiang 24-3 and Xijiang 24-1 mainly derived from the source rocks in Xijiang-24 Wenchang and Enping Formations. The chemical composition of crude oils is determined by the source rocks combination in sags. The oil and gas in the basin features in hydrocarbon accumulation near the source rocks and short distance migration from them.

Key words: mixed oil, biomarker, classification of crude oil, oil and source rock correlation, western Huizhou Sag, Zhu I Depression