[1986nate]

The numbers actually are different for FWD vs AWD. Original ratings were 17city/25hwy for AWD models and 19/27 for FWD. This was revised in 2008 by the EPA for "more correct testing procedures" which they claim was for figuring in running a/c, etc. IMO, it was all a load of crap to drop MPG ratings down so they could include more vehicles in the C4C program. New ratings were 15/23 for AWD and 17/25 for FWD.

In any case, they run the cars on a dyno over different computer controlled terrain and driving conditions. In the Laguna FWD I would regularly see 30-32mpg with the a/c on cruising along at 75-90mph. The 92 I drove back from Florida I was seeing 26-29 cruising at the same speeds.
With my 95 Cutlass supreme coupe which was rated for 29hwy under the original ratings and 26 under revised, I got 32mpg cruising at 85-95 with the a/c on and regularly got 24-26 city. It's all about driving habits and typically I always see 10% better than what they're rated for.