For sure.
To improve milage, the keys are:
1. vehicle weight
2. streamlining
3. engine
4. transmission
Cutting vehicle weight is the easiest way to increase fuel efficiency, as the VW Jetta & Golf show.
One frequently missed method is the use of manual transmissions, which are far better than automatics for several reasons. It is a shame that they are so hard to get these days, nearly impossible to get on "Big 3" made cars except for Corvette.