Why changed gasoline consumption from 17/23 to 15/21 at the BMW
brochure X5 3.0si , Canada and Germany show lower consumption

The 3.0 has more horsepower and the new X5 weighs more. Hence worse gas mileage.

2008 EPA testing changed as well.

is the more weight the 3rd row seat ??

The USA rating agency, EPA, changed the way it measures consumption. Magazines and individual people driving the cars found mpg was worse than the EPA rating. The new EPA rating is supposed to be more realistic of actual consumption.

We test drove a 2007 X5 4.8 with a window sticker that said 15/21 and bought a 2008 X5 4.8 with a window sticker that said 15/19.

I believe it is because the EPA ratings were based on a much slower average speed that was no longer realistic, so they changed their calculations, thus the lower (and more real) mileage estimates.

I feel any suv eats gas.

I saw that the v8 actually gets better mpg than the inline 6. Not by much though.

Ok, Just back from a trip to New Mexico. OKC to Taos and around the beautiful state of New Mexico the computer is showing an over all average of 23.2 MPG and the best I was able to keep on the computer was 26.7 MPG. I will be filling with gas soon. The trip was just over 1400 miles. Speeds from just under the limit to well over the limit....
2002 x5 with the 3.0, automatic and 80,000+ miles. Mobil 1 5w30, tires at 34psi. Sams club prem gas for the most of the trip...

what is the difference in fuel consumption between x5 and 530 diesel