Lt. Sweet supplies are indeed a problem. But i think the current high prices are due to tight gasoline supplies and minimal reduction of demand. We've had a big shutdown season + a couple of major falldowns. That has gasoline on fire and therefore has gasoline crudes on fire (pricewise). Couple that with Nigeria in a real mess and up up and away.
US refiners have been investing heavily in desulph capacity to make ULS Diesel, low S gasoline and to deal with heavier crudes. But they didn't choose to keep the refining industry capacity in glut like it was from 1983-->2000 ish.
