Personally, I go where it is the cheapest. The problem is that here in the PRK, the enviro regs have pretty much put many of the oil refineries out business. Witness, Gulf Oil, Exxon-Mobile, Powerine, so what's left? With refineries that is left, it is pretty much a captive market. The govt has suceeded where big oil has failed, actually created a monopoly, ie if you don't buy from us, who else are you going to buy from. Since we practically have zero competition, the price will shoot up. As the end result we have the highest prices in the USA. The gasoline industry is so tightly regulated by the US EPA, Calif. EPA, South Coast Air Basin, etc that the gasoline is practically the same 99.9% of the time. Notice there is practically zero advertising of gasoline on TV? That is because the gasoline companies can sell every drop the make, with no problem.
Here in the PRK, we have 3 big refinieris that supply all of South. Calif, and some of N. Calif. And the refineries in S.F. supply all of N. Calif. Ultramar/DiamondSharmrock/Superior supplies 95%(I think, don't know the exact %) of the non-branded stations, ie Wall-Mart, Costco etc, and also their won Ultramar station, exact same gasoline from the exact same tanks. Ultramar/DiamondSharmrock/Superior also supplies many municipals and rental car places.