I was talking to a guy who does commercial gasoline tank testing and he says that Shell gas is the best. He says of all the tanks he pulls, Shell is the cleanest. He says it is due to the high amount of detergent that is added to their gas. Second best is BP. Marathon is about middle of the road. Chevron (he says is the worst) tanks are full of sludge and Speedway is right there with Chevron. I know I had an old car that ran best on Shell due to the lower amount of ethanol in it in the 90's. I have always used Shell gas in my mowing equipment since, and have never had any engine trouble at all.