The correct answer to the question

A more coherant report was given by THE CHRISTIAN SCIENCE MONITOR which says:

"Hurting the US economy is a longtime Al Qaeda goal and is one of the reasons the World Trade Center in New York was targeted. They're now striking these oil- related sites in Saudi Arabia in an attempt to keep oil prices high and hurt the US economy," says Saud al-Sarhan, a Saudi writer and researcher who follows Al Qaeda closely.
A statement posted on the Internet and signed by the Saudi Al Qaeda leader, Abdul-Aziz al-Miqrin, claimed responsibility for the Khobar attack.
"Our heroic fighters were able, by the grace of God, to raid the locations of the occupying American oil companies ... which are plundering the Muslims' resources," it said. Mr. Miqrin also criticized the Saudi government for "supplying the United States with oil for the cheapest prices, according to their master's wish, so that their economy does not collapse." A Westerner killed during the operation was dragged though the streets, the statement said."

The article then goes on to explain that 2 of the Saudi's killed in the attack were actually guards manning one of the gatehouses. Makes sense to shoot the guys carrying the guns.