With almost 95k on the odometer and generally accelerating conservatively but driving fast....and I do enjoyblasting aroundthe slowpokes driving in the left lane...
[ul][*]18-20mpg around town[*]24-25mpg on the highway 60-70[*]22-23mpg on the highway 70-75[*]20-22mpg on the highway 75-90[/ul]
I use midrange 89 octane and generally see 370-390 miles per tank. I have pushed it to 405 miles but it took over 18 gallons to fill - and it's only supposed to be an 18 gallon tank.

It also gets much better gas mileage in warm weather (over 50) than when it is below freezing.

 

I have a 2002 A6 3.0 with 84500 miles on it and I get about 16-18 city (I have a 9 mile commute to work, so it doesnt get out on the highway everyday) and 21-23 on highway miles with 89 octane. I love this car!

 

99 A6 Quattro 2.8, I use 93 octane. I get about 16-18 city, 24-25mpg on the highway and I drive @ 80mph. I have 81700 miles on it.

my car says to use no less than 91 octane, can I use something less in the car without damaging the car?
if this is hijacking or whatever you call it please excuse.

 

If you rely on the dashboard mileage computer for your mpg estimates, keep in mind it overestimates byaround 2 mpg.
Mine consistently overestimates by 1.5 mpg.

 

My computer is optomistic by 2mpg. I keep a gas and repair log and always divide miles driven by gallons to get an accurate figure. There's some variation because some pumps cut off sooner and some allow you to overfill. When mine clicks off I try and put in another 1/2 gallon for consistency.

 

I just took my first road trip in my new A6 (new to me). It's an '02 with 86000 miles on it and I went 180.6 miles on 6.46 gallons of gas, averaging 27.96 mpg. I had the cruise set at about 75 and never blasted the turbos hard.

These are actual calculations, the only number that came of the car's computer is the mileage (180.6).

 

mine averages 21mpg. i do mostly highway driving