Fuelwatch has launched a new website which places all the petrol stations on a map with their prices displayed in a location context that makes it much easier to use. You can now see the cheapest fuel within a particular area and zoom out to include more petrol stations, with the list down the left updating with the cheapest locations on your screen. You can also click on the filter at the top to select a particular brand if you have a 4c off voucher or some other discount that you usually use so that you only see that particular brand on the map. It doesn't appear that there is an app but if you go to www.fuelwatch.wa.gov.au on your phone, this map shows up nicely. Click on the bottom right corner on the target circle and you will see the petrol stations around your current area.
This comes as petrol stations started to run on a two week fuel cycle meaning that they don't seem to be dropping to the lowest price until after two weeks have passed. It seems that every two Tuesdays, the price drops to the lowest level before springing back up the next day.