If the number of refineries does not effect the price at the pump as much as I think because you say we have enough refineries already, then why is it every time an accident happens at a refinery that forces them to shut down production those of us in the distribution area for the petrol coming from that refinery are forced to endure higher prices.
If, as you say, we have enough refineries, then a plant shutdown, or the many changes they make every Spring and Fall for different grade petrol, should not effect the price like it always does.
In California at least, they keep attempting to build new refineries or even enlarge the existing ones, just to have the left stop them via lawsuits, liberal judges, and the EPA. They are having a tough time in California just upgrading and maintaining the ones that exist.
The US in total has enough refineries to more than meet our demand.
Individual area have more or often less than the local demand. There is not surplus pipeline capacity and extra pipeline miles to shift production from one normal area of distribution to another when there are major extended unplanned refinery shutdowns.