An explosion at a Pembrokeshire oil refinery has resulted in the death of four people and left another severely injured.
Valero Energy UK Ltd and B&A contracts Ltd have been found guilty in breach of health and safety laws.
Robert Broom, Dennis Riley, Julie Schmitz and Andrew Jenkins died in the explosion.
The charges were related to the duty of care to both non-employees and those employed.
Valero Energy UK Ltd and B&A Contracts Ltd are due to be sentenced on the 2nd of November at Swansea Crown Court.