My two most recent tankfuls have given the following mileage:

over fastish (70-100mph) 315 highway miles, 28.5 mpg;
over 300 fast (lots of acceleration) back road and town miles, 24.5 mpg.

Amazing from a 5 litre, 2 tonne car.

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JJ Rodger
2013 G350 Bluetec
1999 SL 500
1993 E300 diesel T
1990 190