If you're shopping for a full-size SUV like the Expedition, you're probably not too concerned about fuel economy–or at least you shouldn't be. Rear-wheel-drive models are rated at 14-mpg city, 20-mpg highway, while four-wheel drive Expeditions only get 13/18, respectively.
It's always worth considering the use of the vehicle. If you plan to put all three rows of seating to work most of the time, the Expedition's useful efficiency becomes that much better. Keep the Expedition in the garage until it's really needed, and it's considerably greener.
Again, we suspect that Ford is giving the Expedition short shrift because while the F-150 pickup line--from which the Expedition is derived--now has a new lineup of V-8 and V-6 powerplants that have boosted its fuel economy considerably, these powertrains are still missing from the Expedition.