With all the US sabre-rattling vis a vis the Gulf region over the past decades, one would expect that the Gulf is the most important supplier of oil to the US. Well, it is not, Canada is. In fact Canada exports nearly twice as much oil to the US as Saudi-Arabia does.
The diagram shows that the US is in a relatively comfortable geopolitical position when it comes to energy security, as more than half of its supply originates from the western hemisphere, and as such threatened by no one and access is limited only by the scruples of the US military, which is even at shorter supply than the oil involved.
So why all this US interest in the Gulf region? Take a look at this map (see page 9 source, the explosive German army peak-oil study):
After the demise of the USSR, the US is the only political entity left with global hegemonic ambitions. Although the US does not have the resources to occupy every piece of land on the globe, it does have the resources to control access to ca. 3/4 of the world’s fossil fuel reserves (mostly sealanes), confined to a relatively small part of the world (‘strategic ellipse’ as the German army study calls it). Control the oil, control the oil dependent nations.