That's interesting, I know there have been several short periods in time the the US has been energy independent but I guess that could just mean they're exporting more than they're importing rather than refining all their own product.
I'm still puzzled as to why with such a massive refinery capacity, it's geared more toward a type of crude that isn't so prevalent, unless the refineries are quite dated and the product requirement has changed over the years, or possibly the type of oil has changed as older wells have dried up.
That would be an interesting thing to look into.