The last statistic data for reserves in offshore fields have shown that natural gas is more than oil in South China Sea. Proved oil reserves and gas reserves take up 38, and 62, respectively of the total. Among the total proved reserves, the reserves in clastic reservoirs occupy 57,, the ones in carbonate reservoirs do 36, and the ones in pre-Tertiary fractured bedrock reservoirs are 7, of the total. The fields of clastic reservoirs are commonly located in the areas near sediment source. The ones of carbonate reservoirs are mainly distributed in the platform areas away from the sediment source. The ones of pre-Tertiary bedrock reservoirs are mostly in strike-slip basins that are located at the west margin of the sea. The proved reserves distribute respectively in the Miocene rocks(51,), in the Lower Miocene rocks(17,) and in the pre-Tertiary bedrocks (11,). High geothermal gradient and the types of organic matter in source rocks are the reasons that gas is richer than oil in resource and the different types of basins decide that resource is richer in the southern part of the sea than in the northern part of it. The tectonic history and the peripheral paleo-river system controls the reservoir types of fields and temporal and spatial distribution of fields.