BP insisted yesterday that it was confident in booking 80 per cent of its 11 per cent interest in Ormen Lange gas as proven reserves, despite Shell’s announcement on Thursday that it had changed its mind about the gasfield and intends to book just 20 per cent. Norsk Hydro also defended its decision to book 80 per cent of its Ormen Lange gas.

The huge discrepancy forces BP into an embarrassing face-off with the US Securities and Exchange Commission when the oil company makes its annual SEC filing in June. The SEC is pursuing Shell for alleged misreporting of its reserves and cannot afford to be seen as lenient towards one oil company while seeking to enforce its writ against another.

BP will seek to argue that, contrary to what Shell says, it is entitled to use computer modelling techniques to map out the extent of the Ormen Lange reservoir. Sources close to BP indicated that the oil company had chosen to ignore the more specific guidance notes issued by SEC and abided by the spirit of the regulation.

But an SEC spokesman said yesterday that proven reserves still required a proper well test.

The growing row exposes an embarrassing weakness at the heart of the SEC’s regulation of oil and gas reserves. Industry experts believe that the SEC’s rules are outdated — crafted in the 1970s — and not applicable to deep-water offshore exploration. Robert Plummer, analyst at Wood Mackenzie, says: “If you take a strict view of the SEC regulations you end up with an uneconomic project. I don’t think the SEC rules are working.”

Shell’s about-turn on Ormen Lange was based on following SEC guidance notes. Sources close to BP, however, suggest that is not necessary.

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