The most I have gotten is 804 miles on 22.6 gal(20.5 gal tank). Have gotten over 700 miles a couple of times, typically get @ 500 miles mixed city driving.
Damn I should have held out for a CRD. I am getting right at 260 to a full tank. I should say though I deliver pizzas in this every night. Also I try to drive it like it is my old 97 XJ with the 4.0 and 4.56 gears.
stock, mostly city and the wife aka 'lead foot' is the driver, 85K miles on it and overdue for me to replace the plugs which might have way too many miles on them, I've read here elsewhere that's a big effect on MPG with the 3.7L V6.
It's a good solid car, not crazy about the ride of course - I drive a vette and it's almost as stiff a ride but around corners, loosy goosy at the same time, and we put new shocks/struts on just last year. Not a single (knock on wood) problem other than the 6-CD changer fried under warranty and the replacement fried soon after warranty expired - I'm ok with that kind of problem!
I am worried it will become a money pit soon at this mileage but, seeing guys here telling their mileage, seems to be a good vehicle.
3.7 gas engine in my 2005 Liberty, 16-17 mixed city/highway driving, about 19 in pure highway driving... About 365 miles before the light comes on the highway... Synthetic oil, Michelin radials at 35 psi... YMMV
With 19.5 gal tank, skids push bar, roof basket, & OME lifted, and gas here @ $6.20 a gallon, $120 per tank, I really don't want to keep track any more.
When it get down to half a tank I fill it. I think I get about 350 miles to a tank.