I get ~15 on average mixed city / highway driving in my 4.6is.

I see 18-20 on long highway trips depending on hills, wind, speed, etc.

Agreed - for the level of performance in the is, the mpg is not so bad at all. Better than previously owned 3/4t and 1/2t suburban, Titan, Armada, and not even that far off a nissan Murano AWD - but light years ahead of all of these in driving dynamics and power.

I recently got 465 miles on I5 with 3 stops on a 2006 4.8is. I am testing it in mixed conditions (freeway/city) and so far 250 miles and a little less than half a tank left. Range shows 190 miles.

465 divided by 24 gallon tank = 19 MPG. Sounds about right to me.

12 MPG that I'm getting for the 4.8 isn't that bad but I get that same mileage from my 07 exploder too. I think there's something wrong with the Ford.

Uhhh .. nevermind. Seems it's spot on. Found this info. on the 4.6L Ford:
City MPG = 14
Highway MPG = 20

Range still showed 39 miles to empty at 465, but i didnt wanna take a chance.

Try different plugs on your Ford, inflate the tires a little and clean out your maf.

01 X5 4.4
 

My 02 X5 4.4 used to show about 14 - 15 MPG, which also seemed to jive with my hand calculations, however, after a re-build on my transmission 18 month ago after which the computer MPG is now shows 18 - 19. In reality it still is 14-15 MPG so I suspect that the computer has been mis-reading it since the transmission work.

The indy repair shop said there was no way to recalibrate the MPG or that my mileage is better because the transmission is working properly (which I doubt).

If anyone knows if there is a way to easy way recalibrate, let me know. Otherwise, I'll continue to live with it because I am so sick of dealing with all the other repairs on the damn thing (in the last 12 months - air suspension/shock repair, leaky coolant repair, engine seal replacement, broken door handle, broker window, etc.). The only things keeping me in the car are my extended warranty and the way it still drives up the Colorado mountains.

Let's face it - we didn't buy them for their fuel economy. In the UK most E53 X5s are 3.0 Diesel! I chose to buy a 4.4 as I don't do a huge number of miles (and I like the sound of a V8). You guys in the USA are very lucky anyway - petrol prices (sorry - gas to you) here are well over £5 ( $7-50 ish) a gallon!

Yeah, but we don't have mandated 35 hour work weeks either .. or has that been discontinued already?

With the kooks in charge now in our government - anything is possible.....

16.2 average per the OBC in mixed city/highway and at mile high elevation. 12ish towing 2,800 pound camper at highway speed and with 4 bikes on the roof cutting through the air. Worth every $ and cent of gasoline consumed. :D