My friend who has worked for the oil companies for 25 years told me this story. Believe it or not, It all comes out of the same pipe Thats right chevron, texaco, am/pm, union 76 or shell its all the same gas. Even the different octane grades start out as the same gas. there are really only two differences between them all. The marketing and an additive which may contain a fuel conditioner such as chevron's techroline is blended in, usually between the under ground tank and the pump, to boost the octane rating and stabilize the fuel. Usually the difference between the grades is the amount of this additive. Knowing this, I have always run the cheapest gas in my truck. This fuel injected Chevy 350 now has over 250,000 miles on it. Most of them towing my boats or other stuff. I have never had a problem with the engine or the fuel system other than the fuel tank which I had to replace last month. In my boat, I pay for the premium grade because of the length of time that the gas may be in the tank. The biggest thing you can do fo your boat fuel is to install a marine fuel seperator and keep the tanks full when your not using the boat (To limit the condensation) I usually fill up when I'm done fishing. If I wasn't going to use the boat for a month or so I would add an aftermarket fuel stabilizer. I'll ask him about the ethanol thing but the way I understand it, it is in all the gas during certain times of the year. Disclosed or not.