PetroRabigh, a joint-venture with Japan's Sumitomo Chemical, made a net profit of SR50.3 million ($13.4 million) in the three months ending Dec. 31, compared with SR52.6 million during the same period a year earlier. 

"The decrease in net profit during the fourth quarter versus the same period a year earlier is due to a decline in refining margins," the company said in a bourse statement. 

Operating profit for the quarter fell 20 percent to SR53.7 million. 

PetroRabigh started operations at its $10.1 billion complex in 2009. Aramco and Sumitomo Chemical each have a 37.5 percent stake in the joint venture, while the rest is publicly held. 

The refinery, which caters mainly to the Saudi, European and North African markets, can process 400,000 barrels of crude per day, accounting for about 19 percent of Saudi Arabia's total refining capacity.