Undiscovered Oil and Gas Offshore Brazil: Santos, Campos and Espírito Santo Basins

The U.S. Geological Survey (USGS) assessed undiscovered, technically recoverable conventional oil and gas in three offshore geologic provinces on Brazil's eastern margin — the Santos, Campos and Espírito Santo basins. It estimated mean resources of 10.4 billion barrels of oil, 53.3 trillion cubic feet of gas and 1.9 billion barrels of natural gas liquids.

The twelve assessment units in the Santos, Campos and Espírito Santo basins: five in the presalt section and seven in the postsalt section. U.S. Geological Survey.

How the basins formed

The three provinces share a similar history:

• Rifting. In the Late Jurassic, mantle hotspot activity began breaking up Gondwana, and by the Early Cretaceous rifts opened as South America pulled away from Africa. From the Berriasian to the Barremian, lake and river sandstones and organic-rich lake mudstones filled the rifts.
• The sag basin. As rifting waned in the early Aptian, the crust cooled and subsided into a broad basin that collected lake carbonates — later important reservoirs — mudstones and some sandstone.
• Salt. Relief along the Florianópolis Fracture Zone formed a volcanic sill just south of the Santos Basin that the sea periodically spilled over. Evaporation in the enclosed basin left as much as 2,000 m of salt and anhydrite in the late Aptian Ariri Formation. Loading by later sediment soon deformed the salt into diapirs, rollers, "turtles" and other structures that shaped where oil and gas could be trapped and sealed above it.
• Open ocean. Seafloor spreading in the early Albian flooded the basin with normal seawater, and broad carbonate platforms formed. A Late Cretaceous rise in sea level drowned them, laid down Cenomanian–Turonian organic-rich source rocks, and brought sand and mud from the Serra do Mar.
• Uplift. Several phases of uplift from the Late Cretaceous to the Miocene, perhaps hotspot-related, shed river, delta, shelf and deep-sea sandstones and mudstones — major reservoirs above the salt. In the eastern Espírito Santo Basin, Paleogene volcanic rocks of the Abrolhos Bank may have covered source rocks, reservoirs and traps below and above the salt.

Source rocks and the model

The USGS defined a Mesozoic Composite Total Petroleum System:

• Presalt lower Aptian lake mudstones, the main source rocks, with Type I organic matter, organic carbon up to 10 weight percent, hydrogen indices up to 900 mg HC/g TOC and thicknesses up to 300 m. Modeling indicates they are generating oil and gas in the Santos and Campos basins.
• Postsalt Albian to Turonian marine mudstones, possible additional sources — deep-sea marls beside the carbonate platforms and perhaps shales from Late Cretaceous oceanic anoxic events — with Type II organic matter, organic carbon up to 8 weight percent, hydrogen indices up to 700 and thicknesses up to 90 m.

In the assessment's model, oil and gas from the presalt lake mudstones migrated into presalt lake reservoirs, mostly in structural traps, and — where there was no salt in the way — onward into postsalt carbonate platform-margin reservoirs and river to deep-sea sandstones. Oil and gas from the Albian–Turonian shales migrated into postsalt sandstones and carbonates.

Results by assessment unit

Mean estimates, fully risked: oil in oil accumulations and gas in gas accumulations for each unit, with the assessment unit's probability:

Oil fields also hold associated gas and natural gas liquids, and gas fields hold liquids; these are included in the totals below.

Totals

F95 means a 95% chance of at least that amount; F5, a 5% chance.

Sources

• U.S. Geological Survey, Brazil Assessment Team (Schenk CJ, Gelman SE, Hearon JS, et al.): "Assessment of undiscovered conventional oil and gas resources in the Santos Basin, Campos Basin, and Espírito Santo Basin provinces of Brazil," Fact Sheet, with input data in Schenk (2026).