I have achieved 25.8 mpg on the first 700 miles of my recently acquired 2000 XJ8. I must admit a lot of motorway but I have found I get an extra couple of mpg driving on the cruise control, hardly using the accelerator at all. The other way is to have a gas conversion which I had on my last XJ6, This will take about 20,000 miles to pay for itself so if you are doing a large mileage is well worth the investment providing you get a decent system. It will return the equivalent of 34-40 mpg. Hope this helps
