TWO oil exploration workers died yesterday after their vessel capsized in the North Sea.

The men were part of the four- man crew of an inflatable workboat which was servicing an oil survey vessel 15 miles east of Wick.

The identities of the dead men, one of whom is a foreign national, were last night being witheld until next-of-kin had been informed.

The workboat is understood to have run into difficulty while tending cables which tow seismic survey equipment behind the survey ship, the Labrador Horizon, causing the 30ft semi-rigid boat to overturn.

Two of the crew were thrown clear while two were knocked unconscious and trapped under the hull of the vessel.

The crew of a third vessel, the 70ft converted trawler the Mary Ann, which was acting as guard boat to the convoy, raised the alarm at about 2pm.

A lifeboat was dispatched from Wick and an RAF Sea King helicopter was scrambled from Lossiemouth.

Another lifeboat which was travelling from Peterhead to Scrabster also attended the incident.

Wick lifeboat coxswain Walter MacPhee said that, by the time his crew arrived, the four men had already been taken aboard the Mary Ann.

In a desperate rescue operation, the crew of the Mary Ann managed to pick up the two crewmen who had been thrown clear while the third man, who was still unconscious, was also rescued from the water after about 20 minutes.

The crew of the Mary Ann then used a winch to lift up the hull of the inflatable to free the fourth man who was recovered 10 minutes later.

All four men were wearing life jackets when the accident happened.

The two men who had been knocked unconscious were tended at the scene by the Wick lifeboat doctor Iain Johnston.

The two injured men were then winched from the Mary Ann on to the Sea King helicopter then flown to Caithness General Hospital in Wick where they were pronounced dead shortly after their arrival.

No-one from the hospital was able to comment on the incident last night.

A spokesman at Wick police head quarters said that the exact cause of death would not be announced until Monday morning when a post mortem will be carried out.

He said, however, that the deaths were probably related to drowning or exposure.

The two surviving crewmen, who were said to be in shock but otherwise uninjured, were taken to Wick by lifeboat before being transferred to Caithness General Hospital for observation.

Mr MacPhee said the two survivors were badly shocked and suffering from exposure.

He added that sea conditions were reasonable with no more than a metre swell.

He said: ''Given the weather, it was very unfortunate that two of them got trapped underneath the boat.''

Pentland Coastguards at Kirkwall, Orkney Islands said that weather conditions at the time calm, with a south-westerly breeze.

The coastguard spokesman added: ''At this stage we do not know exactly what happened to the workboat, nor how long these men were actually in the water.''

The coastguards have informed the Department of Transport's Marine Accident Investigation Branch in Southampton, which confirmed that an inquiry team is being set up to investigate the accident.

The oil exploration vessel Labrador Horizon had been operating in waters off the Eastern end of the Pentland Firth for the past few weeks.

The streamer cables which the crewmen were tending when tragedy struck are used to send sound waves into the sea bed which are electronically measured by sensitive instruments as they rebound from the earth's crust.

The data is used to give a detailed computer picture of the layers of sedimentary rocks where oil or gas reservoirs may lie.

Labrador Horizon is owned by the Horizon Shipping Company of London and is managed by Inchcape Ship Management of Aberdeen.

Neither company was available for comment on the accident last night.