Government officials and independent analysts are checking for signs of petrol companies palming off Auckland's fuel tax to the South Island, but industry insiders have indicated it may be inevitable.
Transport Minister Phil Twyford signalled that this behaviour "won't be tolerated", but Road Transport Forum Chief Executive Officer Ken Shirley has warned regions might bear the brunt of the tax.
Data shows pump prices in the City of Sails are now cheaper than Canterbury, Nelson, Otago, and the West Coast - despite the extra 11.5 cents per litre introduced in Auckland six weeks ago.
Figures collated from pricewatch.co.nz by economist Sam Warburton reveals that after July 1 - the start date for the tax - the average price of 91 in Auckland jumped from $2.13 to $2.24 a litre.
Z Energy spokesperson Sheena Thomas said "to date, by and large, most of our sites have maintained close to the initial 11.5 cents per litre added on 1 July."