But project partner Rigel Energy of Canada is more revealing about prospects for the block 13/24b Moray Firth find.

Rigel chief executive Don West said yesterday the discovery could hold as much as 900 million barrels of oil, of which 270-300 million may be recoverable.

BG said only that it was to carry out appraisal work to build a picture of the find, while declining to comment on the Canadian's remarks.

"We're planning an appraisal well and that will give us a better indication of what reserves are like," said a BG spokesman.

The company announced the discovery earlier this month, saying it had produced medium-light (32 degree API) oil, flowing at more than 2,600 barrels per day.

Analysts are cautious about prospects for the size of the find.

"We really don't know how big it is," said Tom Ellacott at Wood Mackenzie Consultants. "But the reserve figures seem a bit too high. It's all speculation."

Mr Ellacott agreed that, to some extent, the Moray Firth had been overlooked in the past, though it had produced discoveries like Beatrice and Captain. There has only been a modest amount of drilling to date.

He added that, with Texaco's billion-barrel Captain heavy crude field now producing, Talisman's Ross/ Parry discoveries under development and now the BG find, the area clearly had some potential.

Excitement

BG holds 50% of the Moray Firth find, Rigel 20% and Amerada Hess 30%.

Excitement is also growing in the Norwegian sector that BP may have made a big deepwater discovery.

The company disclosed on Wednesday that samples of fluid taken from a well drilled by the heavy duty rig Ocean Alliance in the Nyk High area had been taken ashore for analysis.

Wood Mackenzie speculates in its May North West Europe Report that the target could contain reserves of around 500million barrels oil equivalent.

Mr Hartley said BP and its Nyk High partners would not be able to test the discovery well yet, as Ocean Alliance had a string of contracts to deal with first.

The next job is to test the Ormen Lange prospect for Norsk Hydro, then to drill the Vema Dome for Statoil, followed work on Shell's Helen Hansen find.