Engen is conducting an internal investigation into a fire that broke out at its Wentworth refinery on Sunday night and left one worker injured.
The injured worker was apparently burnt when asphalt fell on his arms while the fire was being extinguished.
Engen spokesperson Raymond Damon said the worker was treated immediately at the on-site clinic and then discharged.
He said the fire broke out in the vacuum unit, which produces oil from crude in the early stages of the petroleum production process.
The fire had apparently raged for 20 minutes before being brought under control.
The impact of the fire was still being felt and the refinery was currently running at 60 percent of capacity.
Damon said Engen hoped to restore the refinery to full production capacity by Wednesday.
Wentworth community activist Desmond D'Sa said hundreds of people had enquired about the fire because the flames could be seen from a distance.
He said Engen's new open-door policy allowed him and two other community leaders to be taken into the refinery and watch the clean-up process, and investigate the extent of the damage.
"This was the first time that we were allowed to watch the workers clean up because we usually wouldn't have been allowed into the refinery," he said.