A 6 cent increase in 91-octane petrol in the past week is likely the first of several increases to come, according to Automobile Association.
The national fuel price went up by 3 cents last Friday and another 3 cents on Monday to $1.87L.
"I don't think motorists will be too happy," AA petrol prices spokesman Mark Stockdale said.
"When petrol prices were dropping last year, they only dropped by 2 or 3 cents at a time, not as much as 6 cents.
"You would think when petrol companies have to put their prices up because of increased commodity prices, they would put them up by the same amounts they put them down."
In July last year, 91-octane petrol peaked at $2.12L.
Mr Stockdale was unsure if it would reach that level again but said price increases were likely in the next few months.
"Going on the trend for the past couple of years, the prices started to go up about this time as commodity prices went up, and then continued to increase until winter time when they began to drop away again.
Diesel also went up by 6 cents in the past week to $1.12L.
"The petrol companies should be explaining to customers why they also put their diesel prices up," Mr Stockdale said.
"AA doesn't think they were justified in putting their diesel prices up."
Low cost operator Gull led a petrol price war in areas it operated last year.
Other petrol services were forced to keep their prices low where Gull operated to remain competitive - a term AA coined "the Gull effect".
Price of 91-octane fuel in Auckland as of March 15
• Z Energy$1.629
• Gas Alley$1.619