Businessman Denis O'Brien has increased his stake in UK oil and gas exploration company Sterling Energy to 8.13 per cent.

Mr O'Brien spent just under £5.6 million buying 39.8 million shares in Sterling on Monday at 14 pence each.

In September, Mr O'Brien acquired 94.28 million Sterling shares at a cost of £9.4 million or 10 pence each. That gave him a 6 per cent stake and made him the group's third-biggest backer.

He is currently sitting on a paper profit of just under £3.8 million from his share buying in Sterling.

Mr O'Brien's latest share purchase was part of an £11 million fundraising by Sterling to help fund an oil and gas project in the Kurdistan region of Iraq.

The Irishman now owns 27.3 million shares personally and 106.7 million through a company called Baycliffe Ltd.

Sterling is listed on the Alternative Investment Market in London and has a market capitalisation of £231.4 million.

Formed in 2002, it has assets in the Gulf of Mexico, onshore US, Gabon, Mauritania, Kurdistan and Madagascar.

It was chaired until recently by Irishman Richard O'Toole and has raised money from investors here.

In a trading update issued on November 12th, Sterling said its third-quarter net group production averaged 6,100 barrels of oil per day, a rise of 25 per cent over the first half of the year. Sterling's shares closed in London yesterday at 14 pence, down 3.4 per cent on the previous day.