Depends on who owns distribution too.
Gas comes from a refinery owned by big gas companies often times to a terminal (Memphis/Greenville). That transportation in much (most?) of Mississippi is barged in on the River. From there, trucks haul it to a “Jobber” who stores it in tanks and hauls/sells to the gas station.
These days bigger companies control all aspects of the distribution. A lot of jobbers/transportation guys own the store too. So the more hands it passes through, the more markup. And you never really know because most of the “independent” guys don’t own the gas or pumps, they sell it for the transportation guy on consignment.
That alone can account for 20+ cents per gallon despite price wars.