Well, I have a Fairmont and before my last fill up I did 520 kms out of it. Mind you, those 520 kms was done with all grand prix traffic light starts
, a single drive at the maximum speed limited
for a few minutes and a few hard freeway entrances.
That's not too bad if you ask me.
The average petrol use is about 13.3 litres/100km before I filled up and resetted the values.
On the highway/freeway it's about 8 litres/100km sitting on 100km/h exactly. That figure was attained from the instant fuel usage meter.