The Santos Basin, offshore Brazil, is approximately 700 km in width and is probably the largest in area of the basins created by the breakup of the Gondwana supercontinent and creation of the South Atlantic Ocean. The crust underlying the basin was intensively stretched north of a major transform fault that affected both continents. Complex rifting within this highly stretched area created a broad marginal basin in the Santos sector of Brazil not replicated on the African side.

During the opening in the Early Cretaceous, volcanic features bounded to the south of the Santos Basin: Walvis Ridge, Rio Grande Rise, and the São Paulo Ridge. The segmented mid-ocean rift valleys developed as far north as the equatorial Atlantic. Organic-rich shales were deposited in lacustrine environments in the early rift valleys. These synrift shales became the primary source rock for the main hydrocarbon systems present in all the South Atlantic basins. As the separation between South America and Africa continued, shallow-water carbonates were deposited that were later covered by a thick layer of evaporites, creating excellent reservoirs and seals resulting in a prolific petroleum system revealed in 2006 by the supergiant Tupi field discovery. In the relatively shallower waters of the Santos Basin, other gas and light oil accumulations exist in Albian oolitic limestones and Upper Cretaceous turbidites. In addition to the synrift-sourced hydrocarbons, these younger accumulations also received significant contributions from the Cenomanian–Turonian marine shales.