Ok people let me share some knowlege with everyone. I work out at Phx Mesa Gateway Airport where I handle and fuel aircraft. ALL unleaded and ALL diesel fuel are the SAME at gas stations. Now under a govt mandate fuel companies have to put in a fuel detergent into their fuel. I.E. Mobile uses Techron , Shell uses something called " V power". All this stuff is is a detergent/fuel cleaner that every gas station must use. Most people think that if a gas station has the cheapest fuel it must be watered down. Fuel and water just don't mix. And from the fuel delivery guy at work, what happens is a corporation will drill for the oil, then the barrels are  sold off to countrys. Then each country will refine a barrel of oil into fuel,from there we have fuel farms all over the country which is owned by some corporations like B.P. which sells the fuel to corporations like Shell, Fry's, Circle K. Now some gas stations will have the cheapest gas because they bid for the fuel in quantaties.  So if Shell says they will buy 8,000 gallons of unleaded fuel and won't buy another truck load for 2 months will have to charge higher then circle k who might buy 8,000 gallons every 1 1/2 months.  But I have to laugh when I see vehicles fueling up at the Shell gas station paying $0.15 more than the person at Fry's or at the Express stop. All fuel comes from the same fuel depot station ,, each gas station has to place a fuel detergent/additive in the fuel mandated by the Govt. And some gas station corporations use some nice spiffy terms to make the consumer think they are getting a better fuel for their vehicle.