BP and Shell dropped their petrol prices on Monday, giving motorists some relief after raising them last week.
The price of a litre of unleaded fell by 3c to $1.75.9.
Both BP and Greenstone Energy, which owns the Shell network of service stations, say the reduction is due to a fall in the price of international refined product.
A spokesperson for Mobil says the company will monitor the situation.
All major petrol chains raised their prices by 3c a litre last Thursday when the Emissions Trading Scheme was extended to cover the energy sector.
The smaller retailer Gull held its prices over the weekend but put them up on Monday.
