350z's gas mileage isnt that great. mixed highway/city(about 70%/30%) i used to get anywhere between 18-20mpg in my g35 (same motor as the 350z). my friend gets about 22mpg in his 350z doing 90% highway driving. and for comparison, my s2k gets 23-25mpg on the same commute that my g35 got 18-20mpg.