French oil giant Total, British oil and gas major BG, the US' Exxon Mobil, and Russia's Gazprom are likely to bid for Indian exploration blocks on offer in the fourth round of New Exploration Licensing Policy.

"Recent oil and gas finds have changed the international perception about Indian geology. The deepwater blocks, particularly the ones in Andaman sea, are likely to be most sought after by the foreign firms," industry sources said.

Total and BG are courting state-owned Oil and Natural Gas Corporation for joint bidding for few of the deepwater blocks on offer, while Gazprom was talking to gas firm Gas Authority of India Ltd for bidding which closes on September 30.

Exxon Mobil too has conveyed in no uncertain terms its interest in the Andaman deepwater blocks AN-DWN-2002/1 and AN-DWN-2002/2, which are perceived to be 'floating on gas.'

Royal/Dutch Shell was looking at the data before deciding on bidding.

Domestic players ONGC and Reliance Industries, are likely to bid aggressively for the maximum number of blocks.

Both the firms are expected to bid for more than 20 of the total 24 blocks on offer.

Nine discoveries over the last couple of years, including last year's gigantic gas find in the Krishna-Godavari Basin by Reliance, have added over 300 million tonnes of oil plus oil equivalent gas reserves to the country's hydrocarbon base.

Sources said the prime interest this time would be Andaman and Nicobar Islands in Bay of Bengal which are believed to be sitting on vast unexplored natural gas reserves, estimated at around 610 million tonnes.

Besides Andamans, blocks in the Krishna-Godavari Basin, Mahanadi Basin and Mumbai offshore deepwaters hold promise of big hydrocarbon reserves, according to sources.

Besides natural gas reserves, seven gas hydrates bearing zones have also been mapped in the Andaman sea.

The free gas in the region is believed to be of the order of 23 billion cubic metres.

India's domestic gas production at present is around 29 billion cubic metres.

The 24 blocks on offer for bidding in NELP-IV include 11 on-land blocks located in Assam, Bihar, Gujarat, Manipur, Nagaland, Rajasthan, Tamil Nadu and Tripura; 12 deepwater blocks on both east coast (8) and west coast (4) and one shallow water blocks on the east coast.