Gasoline prices regionally

I know there can be many variables in prices of commodities. But gasoline is one that somewhere must have a political component along with an economic one. Having said that, looking at those big numbers on the signs out front make me wonder what goes on come pricing time.

Why, I wonder, does a certain retailer list the following prices per gallon of the same commodity in the following communities:

Huntington: $3.399
Gallipolis, Ohio: $3.149
Proctorville, Ohio: $3.289
Catlettsburg, Ky.: $3.259
Ironton, Ohio: $3.269

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Having said all that, I ran some numbers through Excel. Assuming my car has a 15-gallon tank, it could cost anywhere from $47.24 to $50.99 to fill up, a difference of $3.75, or more than one gallon's worth.

Or, let's say I want to spend $50 for a fillup. I could get from 14.71 gallons to 15.88 gallons. At 20 mpg, I would get an extra 23 miles or so by buying in Gallipolis instead of Huntington. But Gallipolis is more than 23 miles from here, so I gain nothing by making a trip up there just to buy gas.