Reading some of the tips on this web site will save you a fist full of cash (may it be Dollars Euros or whatever). Not only on fuel also on wear and tear of your car.
I know we all drive high end cars gas therefore should not play a role. Still the way we drive does play a role (as we all know) on our gas consumption and maintenance of our cars.
Here is the page of tips some drivers put together ----> Click here to open the page
My average on a long cross country trip last May in my M3 was 10.8 L/100 KM, this was calculated by recording all the fuel and milage. 80% highway at 10% above posted speed limits and 20% town and city driving.