Abstract: Xijiang main sag is one of the low exploration sags in the Pearl River Mouth basin. The existing oil and gas traps have obvious differential accumulation patterns, whose formation mechanisms are unclear. Under the guidance of hydrocarbon accumulation theory of fault basins, the source rocks, faults and cap rocks combinations, reservoirs, migration and accumulation patterns are studied by using geological, geophysical and geochemical data. The subsiding centers and primary source rocks transferred from east to west, from the WC 4 Member to the WC 3 Member and the WC 1+2 Member, in the rifting periods. These transferences control the differences of oil-gas distribution between the east and the west. The mudstones in Enping Formation have good quality and large volume. Vertically, high grade source rocks and the lack of later active faults make the oil and gas accumulate in the lower structural layer more easily. In the area where the the mudstone become thinning regionally or the cap rocks are cut partly by later active faults, oil and gas distribute in upper structural layers. The types of "source-to-sink" controls the quality of reservoirs and impacts on the oil and gas accumulating to the lower structural layer. "Storage" migration is the primary mode of the oil and gas accumulating to the upper structural layer. The lower Paleogene structural layer could be one of the key exploration directions, which are the petroleum system around source rocks of the WC 4 Member in the east and the WC 3 & WC 1+2 Members in the west. In the upper structural layers, explorationist should pay more attention on Zhuhai Formation, and find the potential oil and gas zones with "storage" migration mode around the uplifts.

Key words: Pearl River Mouth basin, Zhu 1 depression, Xijiang main sag, faulted basin, differential enrichment of oil and gas, main controlling factors, accumulation model