Refinery capacity is the bottleneck--we're now importing gasoline because we don't have enough refinery capacity to meet our own requirements.
They are both a problem but cheaper costs per barrel will have an immediate impact on the price of a gallon of gas at the pump.
Not much of an impact relative to building a new, modern refinery facility in California, say.
So if refining capacity is truly the bottleneck then why are the gas prices rising along with the cost of a barrel of oil?