The former boss of Pembroke oil refinery has apologised to the families of four people who died in an explosion at the site in June 2011.
Julie Jones, Dennis Riley, Robert Broome and Andrew Jenkins all died in the blast.
A fifth person, Andrew Philips, suffered severe burns.
The explosion happened when flammable gases inside an oil storage tank ignited.
The families of those killed and injured heard a statement read out at Swansea Crown Court.
In it, Chevron, who operated the refinery at the time, offered their “deepest regrets” and “sincere apologies” for failing to do “what should have been done” to prevent the explosion and subsequent loss of life and injuries.
Mark Ellison QC, representing the refinery, admitted a number of “serious and systemic failures” led to the explosion on 2 June 2011.
Addressing the families in court, the Honourable Mr Justice Lewis said this was a very difficult time for everybody involved in the tragedy.
He said families should prepare for “more disappointment”, as they may have to wait longer than expected for him to reach his conclusion.
At the time of the explosion in 2011 the refinery was operated by Chevron but a deal had already been struck to transfer ownership.
Valero Energy UK, which now operates the plant, and local firm B&A contracts both pleaded guilty to breaching health and safety laws in October last year.
Both are expected to be fined.
The case continues.