What highway gas mileage should one expect from a 1.8 and a 2.5?

318i does about 27 city and 35 highway, 2.5 i dunno

Not a manufacturer's statistic:

According to my car's on board computer, I usually get about 23 mpg on the highway and about 20 around town.

Keep in mind its a 95 325i (auto) and I drive it fairly hard.