Norwegian energy and aluminium group Norsk Hydro cut its estimate of total proven oil and gas reserves by 6.6 per cent today, including a cut of about one third in reserves at its big Ormen Lange gas field.
The cut in Norsk Hydro's estimate of total oil and gas reserves to 2.29 billion barrels of oil equivalent (boe) would be filed with the US Securities and Exchange Commission (SEC) after a dialogue with the regulator, the company said.
"The difference relates to proved undeveloped reserves; there is no change in proved developed reserves," Hydro said in a statement.
Chief executive Mr Evind Reiten said he was "quite confident" of the new figures and said the downgrade did not change the company's expectations of the reserves that would eventually be produced nor outlook for the profitability of the fields.
"This is simply a question of the methodology related to the booking [of reserves]," he told a conference call for analysts. In March, Royal Dutch/Shell sharply downgraded its booking of Ormen Lange reserves to 90 million boe from 256 million because the reserve estimates were based on seismic data not sufficiently backed by physical field evidence.
Hydro's downgrade contrasted with an announcement from Britain's BP, which is a partner in Ormen Lange and which nudged up its proven reserves estimate in a report to the SEC.
Hydro's oil and energy chief, Mr Tore Torvund, had said in early June that the group was unlikely to change its booking of Ormen Lange reserves in its filing to the SEC by the end of the month.