I have about 5500 miles on my 8. I do a good mix of city and hiway driving. I noticed something a bit interesting. My gas mileage was in the 17-20mpg range when I first picked up my car. It got worse (12-15mpg) after my first oil change (3000 miles) and is now back to the 16-20mpg. The one thing I noticed was that when I first got the car, the oil level was right about where it needs to be (I assume it was filled to the proper level). After my first oil change, I noticed that the dealer I went to overfilled the oil. I had to put 1000 miles on it just to get the car back to the top part of the dipstick measurement lines. Now, my gas mileage seems to be back on the positive side. Correlation or coincidence?