Depends what kind of driving you do (highway or city) and if you get on it much. I get 18-20 in normal city driving. I'd say yours is average if you do happen to have a heavy foot.
For mostly city driving, I typically get about 225 to a tank (high teens mpg). The best I've ever done was about 375 miles per tank on my 94GT when it was bone stock, on a loooong highway trip.