Since they all are using additives in their fuel, and since you'll never know exactly what's in each brand's additives, it would be hard to determine which is the absolute best. Often one station is using the same fuel supplier as the competitor down the street.

That said, i'm sure there are differences from brand to brand. But there may also be significant differences from refinery to refinery of the same brand. Also, some additives may be better than others for your car. The best thing to do is find one you like and one that your car seems to like at a price you can tolerate. Otherwise, it can't hurt to mix it up and buy from a variety of stations that seem to agree with your car.

I posted a few weeks ago about a strong sulfur smell from my exhaust after hard acceleration. I had been buying most of my fuel at a Crown station which is a fairly common regional brand in the Southeast and Mid-Atlantic regions. Since then I've tried my local Shell station and so far I haven't noticed the problem (though I haven't done a real good heavy acceleration on the interstate recently). But I think the Shell fuel in my neighborhood may very well have less sulfur content than the local Crown. Ironically, it is Shell that is being sued in Florida for $100M for damages to fuel gauges caused by high sulfur content resulting in the closing of 400 stations during the Memorial Day weekend this year. :shock:

If I had my pick of any 93 octane fuel at the same price I would choose Citgo simply because they were the most convenient and the best price in the neighborhood I used to live in and I never experienced any problems. I typically drive vehicles for at least 150K miles and have never had to replace a fuel injector or catalytic converter or any other expensive component that could be effected by poor fuel quality. I've never experienced noticeably reduced fuel economy or performance either.