Diverrick is right, the base fuel is essentially the same in CA, OR and WA. The East Coast is supplied by one big pipeline from Texas refineries. All the brands use the similar base fuel. Given the cost penalties of gasoline without 10% ethanol, you may think the fuel doesn't have ethanol, but it probably does. You are mistaken if you think a different brand of gasoline will give you better gas mileage. You probably watch too much TV and are influenced by cartoon cars smiling. Really? The brands are differentiated by the additive. The additives are very similar, the more the better. The EPA requires all gasoline to have the minimum amount of additive to keep your engine clean. Additives were not used until about 1985, so your vintage 1965 Cobra never saw gasoline with additives! Right now, Costco adds 5 times the minimum EPA amount. No one else adds more than 4 times. As far as the chemistry goes, Shell has the best additive package on the market now. But the best gas you can buy now is the 5X additive Costco, the rest of the majors (ARCO, BP, Chevron, Shell, Sunoco, 76, etc) are all the same. Even the High Volume Retailers like Safeway, Wal-Mart, etc, add the minimum amount of additive required by the EPA. I wouldn't use them, but I'm biased. Most of the racing fuel has lots of oxygenates like ethanol and methanol. The reason Costco adds so much additive is related to Toyota. Many Toyota owners bought Costco gas and Toyota recommended to their owners to not use Costco gas because the Toyota engine valves were dirty. Costco didn't like that so they upped the additive to more than any other marketer. Like I say, I'm biased, as I used to manage quality of gasoline, jet fuel and diesel on the west coast for a major
oil company (not Costco). Now I just like to drive my Cobra!