The President of Brazil intervened yesterday in a row over the potential size of the country’s emerging but apparently vast offshore oil reserves.

President da Silva said that comments made by Haroldo Lima, the Brazilian Government’s director of oil and gas, suggesting that the Carioca oilfield off Rio de Janeiro could contain as much as 33 billion barrels of oil were “improper”.

Mr Lima, president of Brazil’s National Petroleum Agency, had said earlier that the find in the Santos Basin, 273km offshore, could be five times the size of an earlier, massive discovery in the same region called Tupi. That has estimated recoverable reserves of between five billion and eight billion barrels.

If confirmed, the Carioca discovery would represent the largest global oil discovery in 30 years and catapult Brazil into the top tier of producing countries. Mr Lima was forced to give warning later that the information was unofficial, obtained informally from Petrobras, Brazil’s state oil company. Petrobras, which operates the field and owns a 45 per cent stake in it, was also forced to issue a statement condemning Mr Lima’s assertions, although it stopped short of an outright denial.

Geological surveys of the area are continuing and the results will not be known for some time, the company said. “Petrobras will not declare anything as long as we don’t have a concrete result,” Jorge Zelada, Petrobras’s international director, said.

BG Group, of Britain, which owns a 30 per cent stake in the field, also sought to distance itself from the reports even as its share price rose by up to 8 per cent.

Analysts are concerned about how difficult it would be to develop the new fields. Wood Mackenzie, the oil consultancy, cast doubt on the economic viability of the Carioca discovery saying: “This field is going to be very challenging. If they do develop it, it will be very costly.”

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