Lyttelton Port and Port Otago have appointed an independent advisor to look at a potential merger of the two port's operations.
Auckland-based Antipodes, which is a specialist merger and acquistion company, has been chosen.
Port Otago and Lyttelton Port say they will consider integrating their operations to reduce costs, though each port would retain ownership of their infrastructure assets such as wharves and land.
Separately, a bid by Christchurch City Holdings to increase its stake in Lyttelton Port has been successful.
The council investment arm was offering $2.75 per share for another 2.48%, on top of the 75.68% it already owned.
CCHL says it wants to apply to delist the port company from the stock exchange.