The find, in the Thar desert, is said to contain 155 million barrels of oil, capped with a gas reservoir. According to the Indian petroleum ministry, the discovery more than doubles Rajasthan's known oil reserves to 34 million tonnes from 14 million tonnes.

While it plans to carry out further appraisal drilling before deciding whether the find is commercially viable, Carin said it was confident of the exploration block's potential.

"We see the potential for more of the same size to be repeated across the acreage" which measures "20 or 24 times the size of North Sea blocks," said Cairn Energy director of exploration, Mike Watts.

Having bought out Shell, Cairn Energy is the sole explorer on the block, although it has agreed to give a 30% stake to India's state-owned Oil & Natural Gas Corp if the field goes into production.