The drone attack caused a fire in the industrial area where the large Ruwais refinery is located.
Owner Abu Dhabi National Oil Co. is investigating damage to its facilities. The refinery has a production capacity of 922,000 barrels of oil per day.
According to Bloomberg's sources, the region's four major oil countries - Saudi Arabia, Iraq, the United Arab Emirates and Kuwait - have already reduced production by a combined 6.7 million barrels per day ahead of the fire.
This corresponds to a one-third reduction in production compared with levels before the US and Israeli attack on Iran on February 28 and Iran's subsequent counterattacks on targets across the Middle East.
