Comparethemarket are offering a very helpful tool to help you compare fuel prices in some of the most populated areas of Australia. Sadly doesn't offer my area Newcastle, but it does do most of the major cities: Sydney, Melbourne, Brisbane, Gold Coast, Sunshine Coast, Hobart, Adelaide, Canberra, Darwin and Perth.
The comparison tool lets you compare prices for post codes and lets you choose between Petrol, Diesel and LPG, a very helpful tool to help you save money check it out at comparethemarket.com.au/fuel
Fuel | Compare the Market
Obviously don't drive too far to get the cheapest fuel as that cuts down any savings, check your route before you leave for somewhere and see which offers the cheapest fuel on route. There's more saving tips for fuel and driving in this thread: Money Saving Tips while driving to help you save on fuel.