A Kaiwaka petrol station that State Highway 1's heavy stream of traffic usually goes straight past has nearly doubled its sales since the fuel tax hit the Auckland pumps.
Within hours of the 11.5 cents a litre Auckland region-wide tax being introduced, Shamrock Service Station, 7km north of the Auckland/Kaipara District border, clocked about 150 per cent more custom than usual.
The Caltex station usually sold more fuel to local traffic than the potentially lucrative, but already tanked-up, SH1 traffic.
Yesterday, manager Manpreed Kaur described a ''very busy two days'' since the tax was introduced on Sunday.
''Things are changing right now. We do not know for how long,'' she said.
''But we are the first petrol station after leaving Auckland and the last before going into Auckland.''
Shamrock's 91 unleaded petrol was selling for $2.09 a litre yesterday.
Just south of the border at Wellsford, less than 20km from Kaiwaka, a service station manager said the toll from the Auckland fuel tax had been felt immediately.
He said it was against company rules to give fuel prices over the phone, but confirmed it was at the new Auckland price, and ''we have already suffered".
A spokeswoman for Z Energy said the petrol company was monitoring site volumes closely, but did not expect to draw any firm conclusions around the magnitude of any across-the-border buying for at least a week.
''While it is still early days, we think it is reasonable to expect that some service stations just outside of the border will see an increase in demand.
''We are prepared for this possibility, and don't anticipate any supply issues as a result.''
The Z Warkworth pump price for 91 unleaded petrol was $2.26.4 yesterday.
Auckland prices ranged from $2.20 to $2.35 yesterday. Supermarket spend-related discount vouchers offered some easing.
The first regional fuel tax in New Zealand came into force at midnight on Saturday to create a dedicated revenue stream to improve Auckland's roads and public transport.
Fuel companies and service stations do not give prices over the phone or on websites, but a free app called Gaspy tells logged-on users where to find the cheapest fuel in their area.
Larry Green, who is behind the app which was launched in 2016, said thousands of people had signed up in the past 24 hours.