Cairn Energy Plc of the United Kingdom on Tuesday announced third significant discovery in Rajasthan this year, with gross in-place reserves of 400 million barrels.

The N-C-1 well, north of the historic Mangala find, encountered an oil column of 18 metres gross in the Fatehgarh formation, with an estimated 5.4 metres of net oil pay, a company press release said.

The find comes a month after Cairn said it had discovered reserves of between 130 million and 470 million barrels. In January, Cairn announced it had struck recoverable reserves equivalent to 200 million barrels.

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Cairn said further work was required to gain an accurate estimate of the size of the latest find and of the proportion of the oil which can be economically extracted.

The well is located 12 kilometres north of the Mangala, 70 kilometres north of Saraswati and 300 metres from the present northern boundary of the block.

Unlike previous discoveries, the new find is of heavier oil than previously discovered with a specific gravity of 15 degrees API rather than the 24 to 31 degrees of earlier wells.

Further drilling will take place at the end of May and further appraisal up-dip of this discovery is necessary for confirmation of the oil in place estimate and the associated recoverable reserves, it said.

"I am very pleased to announce our third exploration success in the northern part of the Rajasthan block, where we have three active drilling rigs with a fourth on the way," Cairn Energy chief executive Bill Gammell said.

"N-C-1 firmly establishes the widespread distribution of excellent reservoirs across the north eastern area, which bodes well both for the continued exploration programme and the impending appraisal of existing discoveries,," he said.

Further appraisal drilling on the Mangala and N-A oil fields is due to commence before April end.

Cairn is currently involved in an extensive exploration and appraisal programme across its 5,000 square kilometer onshore exploration block (RJ-ON-90/1) in the Rajasthan Basin.

Cairn holds a 100 per cent interest in Block RJ-ON-90/1. Oil & Natural Gas Corporation has a right to 30 per cent of any development area resulting from a commercial discovery on the block.