I live in Minnesota, and recently gas prices have fallen to new lows - currently a gallon of 87 octane fuel can be had for $1.81 - but it appears my mileage has fallen to new lows as well. I drive an '03 Audi Allroad, and about as soon as the gas prices started to fall, I started to lose mileage. I used to cruise at 70 MPH and get about 23 miles to the gallon, and that's dropped to 20 miles to the gallon. Apparently it hasn't hurt performance, as the car gets up and moves like it always has. I would have thought it was only my car that's acting up, until I talked to a friend and he said the same thing about his '87 Ford Ranger.
I know ethanol has approximately 70% of the BTU output that gasoline does, but it's octane rating is higher. I also know that engines cannot automatically increase the compression ratio, so unless an engine is purpose-built to make power from that, any gains from a higher octane rating are lost, but it will still consume 30% more fuel.
I have not noticed any new stickers on the pumps touting, "Now with More Ethanol!" Is there something else being added to the US fuel supply to water it down and lower the price? (MTBE, anyone?) Is there any research going on because of this?