Verified answer

Never broke 30 mpg, but my 02 Dodge will get 25-28 on the highway. (it has been chipped though.) I will bet with some work with air intake and exhaust/turbo work you could easily get 30+, but is it really worth the extra expense?

Sure, the trade off is expensive fuel that needs to be heated in the winter and exhaust that smells awful. They pretty much all do better then their gas counterparts.