From the BMW website:15/20 mpg


The X6 xDrive35i
Explore the X6 Sports Activity Coupe

Overview
Model Highlights
Features & Specs

Features & Specs
Standard Features Packages & Options Specifications


Weight
Unladen weight4894 lbs
Engine
Liter/type/valves per cylinderTurbocharged 3.0/inline 6/4
Displacement2979 cm3
Nominal output@rpm 300 @ 5800 rpm
Max. torque@rpm300@1400-1500 lb-ft
Transmission
Automatic gear ratios – I/II/III 4.17/2.34/1.52 : 1
Automatic gear Rations – IV/V/Vi 1.14/0.870.69 : 1
Reverse gear ratios – Reverse 3.40 : 1
Final drive ratio 3.91 : 1
Performance
Top speed1130 (150) mph
Acceleration 0-62 mph 26.5sec
Fuel Consumption
Automatic Transmission - City/Highway 15/20 mpg
Tires and Wheels
Tire dimensions – standard 255/50
Type - standardrun-flat-all-season
Wheel dimensions - standard19x9.0