Cheap and cheaper! Please explain the 'huge differences in pricing re gas in various parts of Auckland!

Maybe I shouldn’t be putting this ‘out there,’ because it may cause a rush and end the ‘gains’ I am glad to part of re the prices of filling my car. I seem to have fitted into a comfortable pattern when it comes to gassing up my car. If I hit the pumps in central parts of Auckland I am paying about $1.90 per litre but if I manage my trips carefully, I am able to achieve a full tank for about $1.69 per litre. That is a massive difference and for my car it amounts to about $9 a tank. If one had a larger car the savings would really mount up—maybe upwards of $20 per tank. Spread that over the year and the savings are significant. For me, I have worked it out as more than $250 per year. What is driving this ‘fact?’ Is it that costs are less in the ‘burbs?’ That is the only conclusion I can arrive at. Maybe you who ‘deem ourselves to be economic wizzes’ can enlighten me further. I look forward to your postings. #getagooddeal