Refining costs and profits (14. So back to our martini example: During the refining process, the vodka becomes a martini as other ingredients get mixed in - or crude oil becomes gas.
Price is affected here because there are different formulas and quality standards to adhere to. A branded station - think Exxon or BP - can only buy its contracted brand of gasoline, which boasts a special recipe. An unbranded station, Sheetz or Costco, buys basic, wholesale gasoline, which makes it cheaper, but leaves the station with a less guaranteed supply.

Beyond various brand formulas, there are regional requirements. For example, with the 1990 Clean Air Act, the U.S. Environmental Protection Agency rolled out the first phase of a program that requires "cities with high smog levels" to use reformulated gasoline (RFG), which is more expensive to produce.
This accounts for some of the variance between metropolitan and rural prices. Not surprisingly, California has its own grade of gasoline with a "different set of specifications than the rest of the country," according to EIA's Hamilton.