I stumbled on to this test of several gas brands and actual ethanol content and showing lowest contents seem to be Exxon-Mobil and Shell. Only problem is I don’t see a date on the study in skimming over it although there was a 2017 footnote close to the end. But, kind of interesting to look through if you’re running ethanol in your car.
http://jkswanson.com/STEM17Pres2.pdf
http://jkswanson.com/STEM17Pres2.pdf