Its a different situation in NZ though. Supermarkets for the most part don't own Petrol Stations (excluding a few Pak n Save's which have a BP supplied outlet on site). Other retailers can compete with discounted fuel offerings through the AA Smart Fuel system (which is free for consumers to join and includes discounts at select petrol stations with no purchase required other than the fuel). Sounds pretty fair to me.
The biggest fuel discount I got so far was 6c. But is it anticompetitive for New World to offer flybuys since Z are the only petrol retailer to accept it (since they own it). I usually avoid Countdown no matter what discounts they have, I think they are anti-competitive and can't help themselves. I especially don't like the way the run competing countdowns close to each other or use the Resource Management Act to prevent Foodtuffs developing a perfectly good site. We have basically setup the RMA for supermarket chains to use against each other so its our own fault for not fixing the law.