lol.
I used to do work for a gas station chain, and this discussion came up many times. The answer was always the same...someone would look at the stations near by, and price according to the competition. Also, when the news talked about oil prices going up the owner of the station, or chains would set a price per gallon based on that info and change the prices within the next day or 2.
There was no magic to it. It was do what ever could be done and get away with what you could to increase the prices.
Again, this was at the local level, and not at the ports.