Here is my real world fuel mileage. I've had the car 5 1/2 months, driven 15269.2 miles and used 723.325 gallons of 93 octane and once in a while 92 octane. Overall 21.1 mpg. My best for a tank was 24.03, 364.6 miles, 15.172 gal. These are not estimates from the vehicle but calculated from the amount of fuel I had to replace in the tank. I don't drive slowly though.
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Rich
'96 911 C4 Cab (276,000 1 owner smiles)
'11 X3 35i Black Sapphire/Beige,SAP, CP, CWP, DHP, PREM, TECH, Sat radio, Hi Fi, BMW apps, smartphone, 19" w/mixed performance tires.