Safety is on a "knife-edge" in some parts of the North Sea oil industry, MPs have been warned.
The HSE said prosecutions would be considered
The message from the Health and Safety Executive (HSE) came after two platform fires north east of the Shetland.
HSE chief Geoffrey Podger said prosecutions would be considered as part of the investigations, which would be a matter for the procurator fiscal.
Aberdeen South MP Anne Begg described the claims as "quite a damning indictment of lack of investment".
The comments followed a serious fire on the Thistle Alpha on Sunday.
Mr Podger, the HSE's chief executive, told the House of Commons work and pensions committee: "It would be quite wrong to say whether we will prosecute or not in this case, but what is the case is that there needs to be a proper investigation and prosecution will be considered."
An HSE report earlier this month had already warned that more needed to be done to ensure safety.
Mr Podger told the committee that some rigs were being operated far longer than the period they were initially designed for, without the necessary investment in upkeep and repairs.
"There is this history of, on the one hand, disinvestment in the rigs and, on the other hand, prolongation beyond their natural life," he said.
"The situation is getting very knife-edge in some places. That is what the report shows and it is our responsibility as the HSE to enforce on that basis, and we are prepared to do so."
Labour MP Miss Begg warned: "We potentially could have another Piper Alpha on our hands".
Sunday's fire was followed by two other offshore incidents
She asked the health and safety chief: "Is safety offshore deteriorating? We are 20 years from Piper Alpha. Is the safety regime in the oil commercial sector getting worse or is it gradually improving?"
Mr Podger replied: "It has improved since Piper Alpha, because of all the effort put in to learn the lessons from that."
He added: "The truth is that the whole sector is very challenged indeed on safety grounds and this is partly as a result of financial pressures, not least because the actual pressure to generate large quantities of oil when the prices are high may itself make it more difficult for people to actually do so safely."
Chris Allen, of Oil and Gas UK - which represents North Sea companies - did not agree.
He said: "No-one in this industry is in any doubt about the importance of asset integrity, which is the key not only to the safety of our installations but also to the longer term sustainability of the industry.
"Over the last three years, industry has spent more than £3bn in the area of asset maintenance and we have done much to highlight and shift the focus to process safety and asset integrity management."
A union leader earlier called for urgent action to address offshore safety amid fears that somebody could be killed.
Graham Tran, of the Unite Amicus union, said there had been a series of worrying incidents.
First Minister Alex Salmond's call this week for the Scottish Government to handle North Sea offshore safety in Scots waters was dismissed by Westminster.