The Saudis have a Navy. According to Wikipedia it consists of about 12,000 officers and men, seven frigates, four corvettes and "two royal yachts."
As a comparison, in 2002 there were about 560,000 officers and enlisted personnel in the U. S. Navy. And a lot more ships.
As the Saudis have never lifted a finger to protect themselves (or anyone else) it stands to reason they will not lift an anchor to protect their ships or their oil.
To that point, the BBC reports that "Commander Jane Campbell, of the US Navy's 5th Fleet, told the BBC it had warned shipping companies that the US naval presence could 'not be everywhere'".
Why should the United States Navy be anywhere? Why do we have the responsibility to protect Saudi, Chinese or anyone else's ships on the high seas? If the Saudis want to protect their giant oil tankers, let them send out a couple of those Royal Yachts.
The answer will be for the shipping companies to hire security guards to be aboard their ships to repel boarders. Don't think for one second that major security firms like Blackwater and MPRI aren't, as we speak, training operators to take on the role of "repellers."