I drive mine 4,4 x5 on 14,1l/100km that includes urban and highway. What i have noticed is that the frequent stops will make car consume mutch more fuel, it is a heavy car, and you nead a bit more fuel to get it moving

BTW i am amaised that you can get 12,8 out of a 3,0 X5

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X5 4,4i-06 Current
330Ci Cab-03 2007-2008
MB E55 AMG-03 2006-2007
Z3 2,8 Roadster-98 2006-2007
X3 2,0d-05 2005-2006
320d-99 1999-2005