Now that Coles and Woolworths have been stopped from giving large fuel discounts, the 4 cents per litre vouchers are not worth the effort. It's not worth driving 10 minutes each way to get about $2 discount to fill the tank.
Now, it's best to look for the best prices as you drive around and fill-up when you spot a good price.
In my travels I spotted a bargain at MOGAS @ 294 Marion Road, Netley.
I was looking for good priced diesel and MOGAS was 19 cents cheaper than Coles Express @ Hawthorn. ULP was about 15 cents cheaper. The prices were also much lower than a heavy discounter on Richmond Road.
I check the prices as I pass and MOGAS is consistently a lot cheaper.
The prices were still low when I passed a few days later.
So, if you want big savings, then go to MOGAS @ 294 Marion Road.
Down Anzac Highway, right into Marion, after 2km it's on the left (before Galway Avenue).
I am advertising this to keep a good volume going through the pumps - that way prices will stay low (for me).