Local gas prices

I understand that gasoline is expensive; it ought to be. I understand that gas prices ought to be a little bit higher in my small town than they are in the city. But how much higher? A few weeks ago I noticed a nine-cent spread between gas stations here and a gas station in Aylmer (that admittedly has lower prices than some other stations). Last Saturday the spread was thirteen cents: 115.9 vs. 102.9. Can someone please explain why there’s that much of a difference in price between gas stations only 75 kilometres apart?