We have debated this before.
But having said that, a large part of the problem is not enough refineries. We have half as many as we did in the 70's during the oil embargo days, if you’re old enough to remember, we were also importing about 40% less oil then. We have a NIMBY (Not In My Back Yard) problem in this country. Compound that with the 21 different blends (mandated by the government for specific areas of the country) They are non transforable from one area to another, and requires the refinery to shut down for cleansing before the production of another blend can start.
There is an oilman (meaning someone in the business) here in the BBS. Maybe he can add to this and clarify.