Saudi Oil Minister Ali Al Naimi said oil and gas output was unaffected by the "terrorist attempt" -- the first direct strike on a Saudi oil target since Al Qaeda militants launched attacks aimed at toppling Saudi Arabia's pro-Western monarchy in 2003.
In a statement posted on a Web site often used by militants, Saudi-born Osama bin Laden's group said two of its members carried out the operation.
"With grace from God alone, hero mujahideen from the squadron of Sheikh Osama bin Laden succeeded today (Friday)...in penetrating a plant for refining oil and gas in the town of Abqaiq in the eastern part of the peninsula, and then allowed two car bombs in driven by two martyrdom seekers," it said.
It said the raid was within the framework of efforts by Al Qaeda to prevent the theft of Muslims' wealth by "crusaders and Jews" and to force "infidels" out of the peninsula.
Oil prices jumped $2 a barrel on news of the attack in the world's largest oil exporter, which came a year after bin Laden urged his supporters to hit Gulf oil targets.