KEY POINTS:
The six cent drop in the price of diesel is three weeks overdue, according to the Automobile Association.
Shell, Caltex, BP, Mobil and Gull have decreased the price of diesel by six cents due to international prices dropping.
The latest cut comes four days after diesel fell by 8 cents on Friday.
But AA spokesman Mark Stockdale said oil companies had some explaining to do.
He said the cost of diesel at the pump is now about right but for the past three weeks, it has been too expensive, given the drop in the international price.
"We're surprised it's taken this long for the prices to drop," Mr Stockdale said.
He said motorists could find it confusing that while the Kiwi dollar had dropped, the price at the pump had also fallen and that was unusual.
"Our monitoring of the importing margin shows that with the drop in the refined price and the drop in the dollar, the margin was higher than the average and has been so for the last three weeks," Mr Stockdale said.
He said the price of petrol was "about right".
Diesel is now selling for 165.9 cents at Shell, BP, Mobil and Caltex and 164.9 at Gull.
Shell was the first to move at noon today and spokeswoman Jackie Maitland said it was the sixth drop since July 17.
"We recognise that fuel prices have been hurting motorists and we always look to pass on any savings we can to our customers," Ms Maitland said.
BP spokeswoman Anita Ferguson said BP also moved this afternoon.
She, Caltex spokeswoman Sharon Buckland and Gull's retail business manager Graham Stirk said petrol had not moved because diesel was moving separately from petrol on the international market.
Mobil spokesman Alan Bailey said the price of diesel is determined by freight costs, the strength of the Kiwi dollar, the international price and what competitors are doing.
When asked why the price had not dropped sooner, Mr Bailey said "there are a whole host of things that go into the mix to determine the cost for New Zealand consumers".
