My '06 4.4 now has just under 9000 mi. I'm using 89 octane at the advice and recommendation of my selling dealer, who recommends that fuel for all cars except the M's. I get 14.5-15 in the city and easily do 22 on the highway at 70-75 ACTUAL mph (i.e., 73-78 indicated). On a recent 5000 mile road trip, got as high as 26 . . . . I am well satisfied.

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Sageriders
2011 328, Water [blue], Saddle
2006 X5 4.4i, Sterling Grey/Truffle, Premium, Sport, Cold, Rear, Adj. Ride Ht.
2005 X5 3.0, Sterling Grey/Black, Sport(Totalled!)
2002 330i, Grey-Green Met/Truffle Br. [Sold]