Rescue workers said Friday they had abandoned hope of finding 149 workers missing after an explosion blew apart a North Sea oil rig in the worst such disaster ever.

Seventeen bodies and 64 survivors were pulled from the chilly waters after the blast. Police said at least two Americans were on the rig when it exploded. Their fate was unknown."We, of course, gave up any chance of finding anyone else alive, most regrettably, at sunset last night (Thursday)," Derek Ancona, commander of the Aberdeen Search and Rescue Region, told the British Broadcasting Corp.

More than 100 contract workers refurbishing oil rigs in the North Sea resigned Friday, citing concerns about safety of the offshore industry in the North Sea.

"They felt some action had to be taken, concerning safety," Keith Gibson, an official with the General, Municipal, Boilermakers and Allied Trades Union, told the BBC.

U.S.-based Occidental Petroleum said a gas leak apparently caused the blast Wednesday night on the Piper Alpha oil rig 120 miles off Scotland, but it did not know what caused the gas to ignite.

The disaster is expected to cost insurers more than $1 billion in claims, which would be a record, the Lloyd's of London insurance market said. Lloyd's spokesman David Larner said Occidental insured the rig, plus the costs of any loss of life claims, salvaging the rig, redrilling and pollution.

The rig was still burning. Occidental said Paul "Red" Adair of Houston, Texas, an expert in capping out-of-control oil wells, would try to stop it. Adair was brought in to cap the first blowout on a North Sea rig in April 1977.

Armand Hammer, the chairman of Occidental Petroleum, flew in from Los Angeles and landed at Aberdeen's airport, where flags were at half-staff. He conferred with company heads in Aberdeen before visiting injured survivors at Aberdeen Royal Infirmary.

Hammer told reporters the company was donating 1 million pounds, or $1.7 million, to a trust fund set up for the victims and their families.

The Coast Guard said six oil industry ships, the semi-submersible rig Tharos and one Coast Guard helicopter resumed searching Friday at dawn.

A death toll of 166 would make this the world's worst oil rig disaster, surpassing the 123 deaths when the Alexander L. Kielland platform capsized in Norwegian North Sea waters in March 1980.