The Commerce Commission has indicated it expects to make a decision on whether Z Energy will be cleared to buy the rival Caltex petrol station chain by mid-December.
The regulator has advised it expects to make a final decision on December 18, Z said in a statement.
The petrol station chain said the date is indicative only, and it's still pushing for a November 30 transition date.
"This will enable Z to be well positioned in the event there is a decision earlier than the indicative," it said.
In its application to the regulator, made public this month, Z said its planned $785 million purchase of rival Chevron New Zealand's Caltex-branded network won't drive up prices at the pump because the target doesn't have retail price-setting power and the market will remain highly competitive.
A Caltex factsheet says it has 147 outlets in New Zealand, supplies fuel to the aviation and shipping industries and is a partner in the AA Fuelcard loyalty scheme.
Z is a shareholder in the rival FlyBuys scheme and its website says it has more than 200 outlets.