Ethanol content is supposed to be posted on the pump...
I think it varies from state to state whether it is required to list if gas has ethanol or not. For a while in Oklahoma, it was not a requirement, but people pitched a fit, and now it is.
Sometimes pitching a fit is beneficial! ;-)
If you are not sure what’s in the gas, there is a small device that you can buy at a lawnmower store that will detect ethanol. I think it’s pretty cheap.