Auckland's northwest could soon see a petrol price war

Costco says its administrative office has started taking memberships - as its service station nears completion.

The AA expects it will help increase petrol price competition.

Consumer NZ chief executive Jon Duffy says the company will likely face the same supply chain cost as other fuel providers - but may set different margins.

He says if they're willing to take a lower profit to build up customers - that would be welcomed by many consumers - but unfortunately that's only in Auckland.