NEW YORK, US - US airlines have raised fares, added new fees and surcharges, cut jobs and reduced services - and still find themselves running out of options to counter record fuel prices threatening their survival.

Even mergers, long considered an integral component to the airlines' long-term survival, seem less likely now than they did a few months ago.

While Delta Air Lines Inc has agreed to acquire Northwest Airlines Corp, merging may not be an option for other carriers as cash becomes king in a battle for survival.

'Even at current oil levels of US$130 a barrel, the airlines are involved in a massive survival game,' said Julius Maldutis, president of consulting firm Aviation Dynamics.

Seven small airlines have filed for bankruptcy or stopped operating in the past five months and, if oil prices do not ease by the end of the summer, Mr Maldutis said that several network carriers could file for bankruptcy protection by the autumn.

'You are not going to file for bankruptcy when you are down to a couple of hundred million (dollars) in cash - you are going to file for bankruptcy when you have still got a billion and a half or so if you are going to hopefully survive operationally,' Mr Maldutis said.

Major US airlines have raised round-trip fares by up to US$60 over the past few days as they struggle with oil prices that on Tuesday continued to trade around US$129 a barrel, roughly double where they were a year ago.

Analysts expect the legacy carriers to get through the summer season - bookings remain reasonably strong - but if oil prices do not fall by early autumn, some network airlines could face major decisions involving capacity cuts or bankruptcy protection.

'I think bankruptcy protection is a very high probability at these oil price levels for a few carriers within the domestic arena,' said Brian Nelson, equity analyst at Morningstar. 'Ideally, this industry needs a liquidation. It needs consolidation.' Even James May, chief executive of top US airline lobbying group, the Air Transport Association, has forecast more airline bankruptcies if oil prices do not retreat.

'No one is exempt from the threat,' Mr May said in an interview with Reuters last week, adding that capacity cuts could reach 20 per cent and affect dozens of cities, possibly triggering more calls in Congress to re-regulate the airline industry.

The latest air fare increase is the 13th successful rise in 17 attempts by the major airlines since Dec 20, according to Tom Parsons, chief executive of Bestfares.com, an Internet travel Web site.

'The government is going to end up having to do something,' said Rick Seaney, CEO of airline ticket research site FareCompare.com. 'The airlines are at the end of their rope.' - Reuters