Oil giant Shell has admitted three charges over the deaths of two workers in the North Sea two years ago.
Keith Moncrieff and Sean McCue died in the gas tragedy in 2003
Sean McCue and Keith Moncrieff died on the Brent Bravo platform after being overcome by gas while working on pipes in a leg of the installation.
On Wednesday, Stonehaven Sheriff Court heard Shell admit to three breaches of health and safety rules.
The company confirmed its plea but will make no further comment. Sentence has been deferred until next month.
The charges included failing to carry out suitable repairs to a gas leak in the platform's leg and failing to ensure the safety of the two men.
Mr McCue, 22, of Kennoway, Fife, and Mr Moncrieff, 45, from Invergowrie, Tayside, were working on the platform 116 miles north-east of Lerwick, when the incident occurred in 2003.
Sixty non-essential staff were evacuated from the platform by helicopter after the gas was detected in September and a doctor was flown in from another platform to treat the two, but they later died.
The Brent Bravo is one of four oil production and storage platforms in the UK northern sector of the North Sea that make up the Brent field.
Two of its legs are flooded with sea water. The third, the utility shaft, contains process equipment and allows access to the top of the storage cells and was where the two men were working when they died.
The Offshore Industry Liaison Committee (OILC) said questions remained unanswered about events leading up to the incident and called for a fatal accident inquiry.
The union's Jake Molloy said: "It is no surprise that Shell has pled guilty because by doing so it avoids a lengthy, drawn-out and quite possibly exposed hearing which some operators are keen to avoid.
"This only serves to stifle and prevent the detail of what occurred, both in the run-up to the incident and the incident itself, and these are questions that the families and the workers would really like answered.
"I know the fiscal's office is often reluctant to stage a fatal accident inquiry when a prosecution has occurred, but in this case it is absolutely in the public interest, to prevent this from happening in the future."
The Amicus union also welcomed the guilty pleas but it called for tighter legislation.
The union's offshore workers officer Graham Tran said: "Amicus welcomes the guilty pleas but we are fearful the penalties may not provide sufficient punishment and deterrent for the loss of two lives.
The two men died after a gas leak in a leg of the platform
"It's not only vital that we have corporate manslaughter legislation, it's also vital that it is absolutely watertight and imposes the most severe penalties, including jail terms, on those senior people who have responsibility for ensuring the highest health and safety standards for their workers."
Amicus was part of a delegation to the Health and Safety Executive in Aberdeen back in March 2003 when it raised concerns about a lack of maintenance and other issues on Shell platforms and in particular the Brent Field, including Brent Bravo.
It said it was worrying that no strong action was taken at that time and then only five months later Mr McCue and Mr Moncrieff died.
A Shell spokesman confirmed the firm had pled guilty to three amended charges under the Health and Safety at Work Act in relation to the incident.
He added the company could not give out any further details as legal proceedings were ongoing.