LONDON - British oil exploration firm Cairn Energy, which has announced a series of oil discoveries in India, said Tuesday that oil in place in the Mangala field was estimated to reach one billion barrels, with recoverable reserves of 100-320 million barrels.

The on-shore field, located in onshore northern Rajasthan, was assessed by independent auditor DeGolyer and MacNaughton.

Appraisal of the Mangala field has been completed following the discovery in January, and the final appraisal well on another field, known as N-A, is being tested, Cairn said.

Both the Mangala and N-A fields are planned to come on stream at between 60,000 and 100,000 barrels of oil per day in the fourth quarter of 2007.

"Cairn’s fortunes and prospects have been transformed through major exploration success in Rajasthan. An extremely active exploration, appraisal and development campaign is continuing with the potential to add further significant value," said chief executive Bill Gammell.

Cairn, based in Edinburgh, focuses on oil production in south Asia and has significant exploration and production operations in India and Bangladesh.

It is conducting an extensive exploration and appraisal programme across a 5,000 square kilometre (2,000 square mile) onshore exploration block in the Rajasthan Basin.

Cairn said it estimates that, to date, the total oil initially in place it has discovered in the basin is in excess of two billion barrels, though evaluation of the reserves is at an early stage.