Yes we outfitted our refineries back in the early 80s to move towards the production of heavy-sour which at the time seemed to be what the world would be mostly producing. All that easy to suck up light-sweet was already sucked up so the theory went.

Now our refineries like to have a decent amount of heavy sour added to their feed to operate at peak efficiency. Over the last decade fracking has started to produce just insane amounts of oil in the US. But because most of it is light sweet oil it sells for a high price internationally to countries that didn't invest so heavily into refining heavy sour.

This doesn't mean that we aren't using the oil being produced here... And there are plants being put up in LA specifically to refine the lighter oil.