At the end of the day, you can put trillions of dollars into security but these facilities are mostly above ground. A concerted attack, like they've attacked some of these compounds in Saudi Arabia, a military attack, you can't protect against it.
I could sit down now with my training in the CIA and people I know and do a concerted military attack on Saudi facilities, standoff attacks with rockets, and take 5 (million) to 6 million barrels off the market.