Oil giant Exxon Mobil is offering to sell part of its holding in the Porcupine Basin gas field off the west coast.

Exxon bought 80 per cent of the Dunquin north and south blocks from the O'Reilly family- led Providence Resources in early 2006, which still has a 16 per cent share in the gas prospect.

Yesterday, the multinational's local subsidiary, Exxon Mobil Exploration and Production Ireland, said it is "offering the opportunity for interested parties to acquire a portion of its equity interest" in the basin. It added it had a long-standing practice of reviewing its exploration assets in light of their potential value to the group and other players.

A spokesman told The Irish Times that the company was committed to continuing to explore for oil and gas in the Porcupine Basin.

Exploration companies frequently offer interests in oil and gas opportunities to other parties, as it allows them to spread the cost and risk of exploitation.

Davy Stockbrokers analyst Job Langbroek suggested the offer could indicate that Exxon was planning to begin drilling in Porcupine. "It would be normal practice, even for a supermajor, to reduce one's interest from 80 per cent, when a well is going to cost $100 million," he said.

According to some reports, the Dunquin blocks could hold up to 1,000 billion cubic feet of natural gas. Ireland's requirement last year was 550 million cubic feet.

Exxon will share data on the prospects between February 25th and April 24th and the deadline for offers will be noon on April 25th. Exxon Mobil is the world's biggest publicly-quoted oil and gas exploration company outside state control. It is best known for its Esso, Mobil and Exxon brands of petroleum products.

Earlier this month, it said 2007 profits were up 3 per cent at $40.6 billion. Earnings for the final three months of the year were $11.6 billion.