The most common high-octane gas station chain in the United States is Pennsylvania-based Sunoco, which offers gasoline up to 96 octane. In addition, public auto racing tracks are traditional sellers of high-octane gasoline. Yelp.com offers extensive lists and ratings of high-octane gas stations throughout the United States.
Most gas stations in the United States offer three octane grades: regular (87 octane), mid-grade (89 to 90 octane) and premium (91 to 94 octane), according to the Anti-Knock Index. Sunoco is the only large American chain to offer four grades of gasoline.
The octane rating of gasoline is a measurement of performance. The higher the octane rating, the more compression the fuel can withstand before igniting. Higher-octane gasoline is mainly used in the engines of luxury vehicles and sports cars, but even in these cases, its usefulness is questionable.
The Federal Trade Commission warns against unnecessary purchases of high-octane premium fuel. The FTC website encourages car owners to listen to their engines; if the engine doesn't knock when gasoline of the recommended octane is inside it, that octane is acceptable. High-octane gasoline doesn't prevent engine deposits from forming any better than regular octane, according to the FTC. Nor does it help remove deposits or clean a car's engine.