I just took a 3200 mile trip, 90% highway, 6 passengers, the rear cargo space stacked up to the headrests with luggage, AC on 100%, cruise control used when conditions allowed. Speed was between 70 and 75 mph.
Roads were mostly flat but there were a lot of places that required the transmission to get out of overdrive to maintain the 70 mph speed.
The best mpg for the trip was 25, worst was 24.
This is in line with the EPA figures of 17/25/20 (city/highway/combined).
I am happy with the mpg from this 2008 Ody.