Abstract: The Campos and Santos basins are considered as the most important oil industrial base of Brazil. The two basins as a whole are one of the four major regions around the world rich in deepwater hydrocarbon. According to the statistics by the IHS Global Energy database (2010), The Campos and Santos basins contributed 83% of the oil and gas reserves and 62% of the oil and gas production in Brazil. The two basins are located along the southeast coast of Brazil, both belonging to Atlantic-type passive marginal basins superimposed on the Mesozoic rift basins. They are next to each other, have experienced similar tectonic evolutionary history and under similar petroleum geological conditions. However, the hydrocarbon accumulation pattern of the two basins are obviously different. In the Campos Basin, oil and gas primarily accumulated in the Upper Cretaceous-Miocene turbidite sandstone reservoirs characterized by heavy crude oil, while in the Santos Basin, hydrocarbon is mainly found in the Lower Cretaceous carbonate reservoir characterized by intermediate oil, light oil and natural gas. We made careful study on the two basins in this paper with special attention to the difference of basement structure, oil and gas fields distribution pattern, fluid properties, accumulation elements and plays. Our results show that spatial differentiation of oil and gas distribution owes its origin to salt layer. And the basement structure and sedimentary sequence formed in the drifting period contributed a lot to the deformation and distribution of salt layer.