Production was shut down, and 38 workers evacuated, at a North Sea gas platform following a leak.
The non-essential staff were taken off the North Everest installation, operated by BG Group, on Tuesday.
The platform, which is 145 miles east of Aberdeen, suffered a power outage moments after it was shut down after the leak had been detected.
The Health and Safety Executive (HSE) has launched an investigation.
A BG Group spokesperson said there was "no risk to personnel or environment".
Power was later restored to the platform.