Hello, I have just purchased an X5 40 xdrive. I am not sure what to make of it yet. I have owned many BMW cars for a long time and X5 is my first 4x4 from this manufacturer.I find fuel efficiency a bit bad. BMW advertises 37.7 mpg but I get 15 mpg. I consider my self to be a safe driver. i find the difference between what they advertise and what I get a bit high. I also own a mercedes CLS 350 CDI which gives me 35 to 40MPG which is very close to what they advertise. Can someone please share their thoughts with me. Thanks A