[mrv]

http://pressroom.toyota.com/photo_library/display_release.html?id=2004prius_prelim_s

Note that they consider it a mid-size vehicle instead of a compact. These specs still don't show gas milage, but the horse power ratings are there as are the vehicle dimensions.

http://www.fueleconomy.gov/feg/info.shtml#sizeclasses

"The size class for cars is determined by measuring the interior volume ....
Compact Between 100 and 109 cubic feet of passenger and luggage volume
Mid-Size Between 110 and 119 cubic feet of passenger and luggage volume"

According to the document you listed,
the current generation Prius has a
total interior volume of 100.4 cu. in.,
while the new 2004 Prius has a total
interior volume of 110 cu. in.