It's a local thing and varies by state. You and your profile don't mention where you are so a specific answer is not possible. Do a search on Ethanol and you'll see where this has been discussed at length. In OK, the state requires gas pumps to be labeled if they contain Ethanol. Many states do not require this.
I live in Bay Are, CA. One of the Shell gas station near by my house listed might contain 10% Ethanol, but the 76 and Valero did not list any thing.
In CA, all gas are mixed with ethanol as required by CARB. Some gas station may not have the label on the pump, which they should, and you can go in and ask the cashier.
