Ironically, however, it could lead to higher prices elsewhere. If a lot of motorists tanked up in Whangarei, Bay of Islands service stations might raise their prices to make up for lower volumes.
Last week competition in Whangarei was even hotter than usual, with Gull dropping its pump prices by 10 cents from Thursday morning until noon on Friday.
Consumer NZ senior writer Bill Whitley agreed that the single biggest factor in petrol price differences was competition, although volume and distance from a port played a part.
"Like most things, people will charge what they can get away with," he said.
BP spokesman Jonty Mills said all Northland's BP stations were supplied from Marsden Point at the same wholesale price. A delivery fee based on volume and distance from Marsden Point was relatively small.
Some BP service stations were directly owned and operated by BP, so the company set the pump price.
Most, however, were independently-owned, and the owner set the price.
In areas with little competition they could choose to set a price above the national average. In places with fierce competition they might sell below the national price and hope to make up for it by selling a greater volume.