The price of petrol fell 14 cents a litre in September, while a litre of diesel became 7c cheaper.
The Automobile Association says in the main centres the cost of a litre of 91 octane fell from $1.69 to $1.55, while the price of a litre diesel dropped from $1.07 to $1.
The AA says the lower fuel prices are due to the strengthening New Zealand dollar, which rose nearly 4c against the US dollar in September.
However, savings at the pump will soon be pegged back by higher taxes.
From 1 October the excise duty on petrol rose 3c per litre, while diesel road user charges have been lifted by varying amounts depending on vehicle weight.
Some oil companies say they will wait as long as possible before passing on the increase to customers.