The Jones Act, as well, effects domestic oil shipments. It only allows US built, flagged and US citizen majority crewed vessels to do inter US oil shipments. So, say a Gulf refinery wanted to ship to New England, it would have to be on a US ship, and there aren't that many that fulfill the requirements.
That multiplies the problem. Say a foreign tanker can drop off oil in an open US port. That port may have a surplus of oil, but it can, basically, only be carried by train or truck to other parts of the country, if they're not on an inland waterway that handles barge traffic.