On Friday, bombers in two cars attempted to attack the facility but were stopped by guards. One car exploded damaging a pipeline, Al-Arabiya TV reported.
It was the first such attack on an oil facility in the kingdom, which has waged a fierce three-year crackdown on insurgents and suspected al-Qaida fighters. There have been previous attacks on oil company offices, but not on a facility where oil is present.
The blast damaged a pipeline at Buqayq, a large complex that processes crude oil 70km southwest of the oil hub of Dammam on Saudi Arabia's Gulf coast, the Saudi-owned Al-Arabiya said.
Oil stopped flowing briefly but then resumed, it reported.
Security guards opened fire on the explosives-packed cars as they attempted to drive through the facility's gates, the Saudi-owned television network said. The two cars bore logos of Aramco, the state oil company that owns the facility.
One vehicle was stopped, and two people inside it were killed. The other vehicle exploded when the guards fired on it, the Al-Arabiya correspondent said. None of the guards was hurt, he said.
An oil official confirmed the explosion to The Associated Press but said he did not know the cause. The official spoke on condition of anonymity because information was still preliminary.
Lieutenant-General Mansour al-Turki, the Saudi Interior Ministry spokesman, told AP in Cairo: "I have no information. I am following this up."