Could be real low octane fuel with ethanol to prop up the octane rating.
IIRC anything over 10 % Ethanol content is not legal to sell in pump gas. E 85 not included in that .
There is a presumptive to test for the amount of ethanol in gasoline. Just google it. Then go down to the station and get a cup of gas and do the test.
It probably isnt the ethanol, its probably really crappy gas mixed with ethanol, and probably more than legally allowed.