Forsyth Barr was forecasting a first-half operating profit of $125 million, up $24 million on the previous corresponding period.
The reported profit was set for a 53% increase to $69 million and the interim dividend was expected to rise to 9.9c per share, a 29% increase.
Broker Suzanne Kinnaird said on Monday the 2016 first-half would be a stark but positive contrast to the first-half in 2015.
Last year, refinery margins were weak, to the point Z had to provide support.
This year, the refinery margins had been above the cap, meaning Z had enjoyed ''discounted'' processing fees.
Forsyth Barr's estimate of the first-half refinery gross margin contribution was $30 million against $7 million in the pcp.
Fuel margins had also been stronger but were partially offset by weaker volumes.
''Fuel margins are the key value driver and have trended upwards from unsustainable low levels over the past five years. We do not expect margins to increase materially from current levels.''
Fuel demand was generally inelastic, Ms Kinnaird said.
While it was an important value drive, the variability was less than margins. But maintaining a minimum volume level was important for supply chain economics.
The industry was an oligopoly dominated by Z, BP, Mobil (Exxon) and Caltex (Chevron).
Gull featured in the upper North Island market. Z's New Zealand-centric business model provided it with flexibility and a market-leading position, she said.
Z was seeking to acquire Chevron for an all-inclusive price of $863 million.
''We believe the transaction provides Z with material synergy benefits and long-term growth opportunities. While we are expecting Z to provide a knockout result, the key focus will be an update from Z's perspective on the Commerce Commission clearance process. The commission is aiming to provide clearance, or otherwise, before Christmas and we should get a clearer view on whether that is likely or not.''
Forsyth Barr had an outperform rating on Z and a share target price of $7.10, Ms Kinnaird said.
