The 2010 Ford Escape Hybrid currently has the best gas mileage at 31 mpg in the city and 34 mpg in the highway. The same mileage is available in two wheel and four wheel drive.
Really if you are concerned about mileage then you should stay away from trucks or SUV's. The only ones that get kind of good mileage are the hybrid ones. Their price however is much more than the normal model and mileage is still not as good as a smaller wagon or crossover.
