Petrobras has declared as commercial three pre-salt oil accumulations in unlicenced Santos basin acreage off Brazil, saying the Guara South, Tupi North-east and Florim field add a combined 1.214 billion barrels to the company's already formidable reserves.
The Brazil state-led company's latest move, to be considered by the country's ANP oil regulator, adds to resources already booked in open acreage.
A special agreement signed earlier this year gave the company rights to produce as much as 15.2 billion barrels in premier pre-salt finds in the area known as the Cessao Onerosa.
"With the declaration of commerciality...the formal process to review the transfer of rights agreement will get under way on a block-per-block basis, taking into account the technical and economic premises of each area," Petrobras said in a statement.
The company has already declared commerciality at the Franco and Tupi South fields, where an agreement to formally transfer rights to Petrobras is still pending.
Iara Surround is the last block in the area that has not yet seen a declaration of commerciality, but that process is expected to be wrapped up by year's end.
Petrobras confirmed the resources at the pre-salt trio following an exploration programme that included the drilling of five wells to appraise the finds, three formation tests and one extended well test.
Tupi North-east, to be renamed Sepia, is expected to start commercial production in 2018. Florim, now to be called Itapu, is expected to get under way in 2020.
The two fields are between 185 kilometres to 260 kilometres offshore Rio de Janeiro state at water depths between 1850 metres and 2250 metres.
A start-up date for Guara South, to be renamed Sapinhoa South, will be determined in Petrobras' 2015-2019 business plan, the company said.
That field lies some 320 kilometres off the coast of Sao Paulo state at a water depth between 2,200 metres and 2,250 metres.
Petrobras reported reserves of 13.12 billion barrels of oil equivalent as of year-end 2013, an increase of 1.9% from year-end 2012.
Critics, however, have fiercely challenged Petrobras on whether it can execute on its ambitious goals of developing heavy pre-salt commitments on its own, and have urged more involvement from partners.