The Guara find in Brazil's Santos Basin by state-run oil firm Petroleo Brasileiro SA (PBR), BG Group PLC (BG.LN) and Repsol YPF SA (REP) represents a massive discovery, a person familiar with the situation said Thursday.
Guara is estimated to contain between 3 billion and 4 billion barrels of oil equivalent, or BOE, in hydrocarbons, this person said.
In June, the consortium said it found oil at Guara in the BM-S-9 block, but so far hasn't made an official reserve estimate. Petrobras holds a 45% operating stake in the field, BG 30%, and Repsol the remaining 25%.
A press official for Petrobras' Chief Executive Sergio Gabrielli declined to comment. Petrobras in a filing to Brazil's stock market regulator said it does not yet have "conclusive data about the volume of recoverable oil" at Guara.
Brazil's Gazeta Mercantil newspaper reported Thursday that Petrobras will soon release a reserve estimate for Guara. It potentially has 3 billion to 4 billion barrels in reserves, Cristina Pinho, a general manager at Petrobras' exploration and production area, was quoted by Gazeta Mercantil as saying.
Late Wednesday, Repsol Chairman Antonio Brufau said the company made two large oil discoveries, without elaborating further.
BG earlier this month said the consortium is fast tracking plans for a 100,000 barrel-a-day pilot scheme at both Guara and the nearby Iara discovery, with the objective of achieving first production in 2012.
The companies have already released an 3 billion to 4 billion BOE reserve estimate for Iara.
At 1348 GMT Repsol shares were up EUR0.55, or 3.7%, at EUR15.16.