Husky Energy sent 33 offshore workers ashore Sunday because of a buildup of sour gas in a pair of storage tanks aboard White Rose production ship.
A Husky spokeswoman said the sour gas buildup occurred last week due to a faulty circulating pump.
A new pump was installed last weekend, but efforts to vent the gas into the air failed because of light wind conditions at the Grand Banks oilfield.
In the meantime, Husky said it has stopped all outside deck operations until it can vent the gas.
Fifty-three workers remain aboard the production ship doing inside work. Oil production continues.
Husky expects to reduce the sour gas buildup and return to normal operations by the weekend.
Sour gas is hydrogen sulphide, which smells like rotten eggs and is colourless, flammable and toxic. It results from decaying organic material, and occurs naturally in crude oil and natural gas.
The sour gas buildup occurred when a pump malfunctioned. That pump circulates a chemical in the two storage tanks, which contain produced water from oil wells.
The chemical reduces the amount of organic material in the tanks.