THE North Sea oil industry has been thrown into turmoil after a major US firm revealed it may pull out of the UK, selling off its significant reserves.

Apache Corporation, the North Sea's third-biggest producer behind BP and Royal Dutch Shell, said it was considering the move in a bid to focus its attention on American shale gas projects.

The firm, once seen as the saviour of the North Sea, confirmed a sell-off is one of two options - the other being the creation of a separate international firm that would take in all of Apache's ventures outside the US. A spokesman for the firm confirmed this could lead to more investment in the UK site, however, industry trade union RMT said it would be a "severe blow" if the company decided to press ahead with withdrawal.

Apache CEO Steve Farris said: "Apache continues to evaluate the separation of its international business through capital markets or strategic transactions.

"The company is now evaluating the separation of its international portfolio via the capital markets. In addition, the company is evaluating strategic proposals for specific assets from parties attracted by Apache's asset quality and track record. The objective is value growth maximization for Apache's shareholders."

Reports yesterday suggested Apache had already instructed Goldman Sachs to find a buyer for its North Sea sites, with a "teaser" document featuring reserves such as Forties and Beryl fields being sent out to prospective buyers.

However, an Apache spokesman denied this, saying the oil firm is still in the process of looking at both options.

Jake Molloy, RMT regional organiser, said any decision to pull out of the North Sea would be a "big shock" to the UK industry and a "severe blow" to everyone working in the sector, especially Apache employees and those providing contracting services to the firm. He claimed that other firms surrounding the Forties site who pump their oil and gas into the Forties pipeline system would also be hit by any decision to sell up.

Mr Molloy added: "The company only recently opened its new multi-million pound headquarters on the outskirts of Aberdeen, a state-of-the-art facility, and that, along with the not-long purchased Beryl field, served to suggest Apache were here for the long haul."

The Apache spokesman said the creation of "Apache International" would allow the firm's ventures outwith the US, including in Egypt and Australia, as well as the North Sea, to take control of their own income and expenditure.

He said this could lead to more investment in the North Sea, but added that the firm is already investing heavily in the UK market.

Mr Farris added: "In the United Kingdom North Sea, Apache is the most efficient oil and gas operator, with operating efficiency above 90 per cent compared with the industry average of approximately 60 per cent. Apache has revitalised major, mature assets acquired from other companies, including Forties, the largest oil field in the UK.

"In addition, Apache has pursued a successful exploration strategy resulting in the development of multiple new fields.

"Apache recently finalized the commissioning of a new platform in the Forties field this year, at the time when the field was expected to enter decommissioning before Apache gained operatorship."

A spokeswoman for industry body Oil & Gas UK said it was not in a position to comment on the "commercial decisions of its individual members or speculate on how these might affect future operations".