The Health and Safety Executive (HSE) has partially upheld claims that Shell was not doing enough to ensure safety offshore.
Unions had raised HSE concerns over worker safety
The OILC and Unite Amicus unions had asked the HSE to investigate following complaints from their members.
This focused on manning levels on Shell installations, workloads and the attitude of management.
The HSE said some procedures had needed improvement. Shell said the investigation was continuing.
An executive spokesman told BBC Scotland: "It was quite a complex complaint covering a range of issues, we spent some time looking at it and went offshore.
"The investigation concluded that aspects of the complaint were justified.
"Procedures were not working as well as they should have done. Shell has taken action to address the matters."
Graham Tran, of the Unite Amicus Union, said he believed Shell should leave the North Sea because it has "no credibility".
He said: "If they want to leave UK waters then good riddance."
Shell said the company was co-operating fully with the HSE in addressing any concerns they may have.
"We continue to keep our staff and the HSE informed", a spokesman said.