From memory, petrol prices, as soon as you leave the city increase. So small country towns, petrol is often more expensive. Probably cause they have to transport the petrol further from refineries.
Some small country towns are no where near a large country town, so sometimes it might be better to pay more than to use all the fuel up in one trip.
I can remember travelling somewhere way out in western nsw, near the boarder and the cost was nearly $2 a litre!!
Edit: Sometimes the country town can only support one petrol station - but is usually like a general store place - where you can literally buy anything. So monopoly increases petrol prices as does the distance from the city.