A couple of statistics for our 3.2 V6 petrol (with 95 octane fuel):
After 500+km of City & Suburban driving I got 10.2 litres per 100km.
After 190km (2.5 hours) of Country driving I got *8.6 litres per 100km.
* = 30 minutes of that was getting through Melbourne City with Air Conditioning on (as it's 40c in Victoria). Air Con stayed on throughout the entire 2.5 hour trip.
For a 3.2 litre petrol V6 with a Full Load in Summer Heat with Air Con on, I'm happy with that