Fuel companies Gull and NPD have completed their merger after clearing regulatory hurdles earlier this year.
The combined entity would be known as NPDGull, while the NPD and Gull sites would remain under their existing brands.
NPDGull said the two brands would benefit from operating under a larger scale business.
To mark the merger, NPDGull launched a national commercial fuel offer, extending the acceptance of the NPD fuel card across the majority of its combined 240 sites.
The group's chief executive Barry Sheridan, said further investments were planned to improve the competitiveness of its offer and quality of service.
"We'll significantly enhance the size of our North Island operations, enlarging our delivery fleet, acquiring more storage tank options, and bring on new team members in our operations and sales areas to leverage the strength of our network and supply chain," said Sheridan.
"From 'Port to the Pump', across the North Island, we'll control every step, improving the resilience of supply to our sites, and to customers in industrial and remote areas."
Under the merger, NPDGull would sit under a parent company called Astra Energy Group.
The South Island-based Sheridan family, previous owners of NPD, controlled half.
Australian private equity firm Allegro Funds, former owner of Gull, owned the other half of the combined entity.