Two companies have pleaded guilty to breaching health and safety laws in connection with an explosion at a Pembrokeshire oil refinery which killed four people.
Dennis Riley, Robert Broome, Andrew Jenkins and Julie Jones died in June 2011 when an oil storage tank exploded during routine maintenance work.
Another man was left with serious injuries.
At the time of the incident the refinery was operated by Chevron Limited, but ownership changed in August 2011.
Today Valero Energy UK Ltd and B&A Contracts Ltd appeared before Haverfordwest Magistrates court.
Both companies pleaded guilty to two charges under the Health and Safety at Work Act.
The charges relate to providing a duty of care to both employees and non-employees.
They are due to be sentenced on 2 November at Swansea Crown Court.