The type of driving has a MASSIVE impact on fuel economy.

My subaru forester will just stretch a tank to about 500km around town. After a trip to Canberra and back, where it was filled up half way there, it's done 520km and still has at least a quarter of a tank.

My father would swear by the fact that a regular freeway trip for his car would help its fuel economy even when it's just running around town. He used to call it letting the car "stretch its legs" and it did seem to make a difference. His fuel economy improved, not just for the tank that did the freeway trip, but for a few afterwards as well. Might just have been that car, haven't put it to the test myself. I don't keep records as accurate as my father, either - he has a little book in the glovebox where he records the date, the km travelled and how much fuel he's put into the tank. Of course, he always fills the tank completely every time he goes, doesn't work if the budget is tight and you can only put say $10 in to get through the next couple of days.

BW