Shell, BP and Mobil, Chevron have cut retail petrol prices by 5 cents a litre.
Monday afternoon's cut came three days after fuel companies dropped prices by 8 cents a litre.
Shell was the first to act, followed several hours later by BP and then Mobil and Chevron.
All are now charging $1.76.9 for 91 petrol.
Gull and Challenge have also cut the price of 91, charging between $1.73.9 and $1.75.9.
The price of diesel has been left unchanged.
Shell says petrol prices have now dropped by more than 40c since mid-July. It says falling crude oil costs and a stabilising New Zealand dollar have helped lower prices.
Mobil says the lower prices are a reflection of the movement in crude oil prices and competition among companies.