Refining New Zealand wants to dredge Whangarei harbour and realign the channel to the Marsden Point oil refinery so it can bring in bigger ships.
The company has started a series of studies on the impact of dredging on tidal flows and sedimentation, marine mammals, recreational fishing and the seabed.
Chief executive Sjoerd Post said the company hoped to lodge a resource consent application by early next year.
Meanwhile, he said lower oil prices were helping to keep a lid on petrol prices, which was in turn driving consumer demand, earnings and profits.
The rise in demand around the world had not stimulated plans to build new refineries, as in the past, which favoured established players such as the Marsden Point refinery, Mr Post said.
And he said it was too soon to say whether the company would match last year's strong $151 million profit, which was out of the ordinary because of high refining margins and a low New Zealand dollar.