I have been discussing the Ethanol buzz in class over the last few weeks. In most older cars, I'm assuming pre 2000, I have been given advice not to use more than 10% because it will eat away the plastic fuel lines over time. The only benefit of using ethanol over an octane blend (petrol) is that it burns much cleaner. The chemical stucture has of ethanol has an OH group at one end of the hydrocarbon chain, as opposed to octane which is all hydrocarbon. What this means is that when burning ethanol, you have already oxidized one end of the hydrocarbon chain and when you go to oxidize (burn) the rest of the molecule, you are only going to get approximately half of the combustable energy as normal petrol. Thus giving you less power and worse gas mileage. In other words, the only benefit of using ethanol is that it is better for the environment.