More competition is needed to cut petrol prices - and somebody should petition Gull to expand, Transport and Energy Minister Simon Bridges says.
A leading competition expert has warned petrol companies co-ordinate prices, and that is likely to worsen when Z Energy takes over Caltex.
But Mr Bridges said the evidence showed there was "workable competition" in the market.
"But, like electricity a few years ago, would we benefit from more competition? We absolutely would.
"And someone should take a petition to Gull to get them moving even more around the country, because where they go, the prices fall."