Why are the Gulf states buying? Partly of course because they have a lot of money burning holes in their pockets: With high oil prices they have accumulated vast hordes of foreign currency. However, their main immediate motive appears to be fear of a hegemony-minded nuclear Iran and, closely related to that, fear that Israel might attack Iran--and that Iran might then retaliate against them, because of implicit or explicit cooperation with Israel.
You don't have to worry; only 15% of our oil comes from the Middle East; It is Japan and Europe that are deeply dependent on the Gulf states oil. You may ask when the Gulf states plan to end there buying spree; we the answer appears that they are not going to stop any time still. With experts saying that Israel is not going to attack Iran and our absence of action. (despite King Abdullah Bin Abdulaziz of Saudi Arabia asking the US to attack Iran in his last visit)
source: IEEE Spectrum