I have never heard of 97 or 98 octane fuel in the US at any regular gas station. Most will only go up to 93 or 94 octane, and if you live on the West Coast I believe it is 91 or 92 octane as "super" gas. Which is equivalent to Super-plus in Europe.
Above 93/94 octane in the US, you have to go with a specialized racing gas, which in most cases is not going to be available at a typical ARCO/Shell/Chevron/Valero/Costco/Sinclair/Phillips66/Texaco/Sunoco/whatever station pump.
Above 93/94 octane in the US, you have to go with a specialized racing gas, which in most cases is not going to be available at a typical ARCO/Shell/Chevron/Valero/Costco/Sinclair/Phillips66/Texaco/Sunoco/whatever station pump.