Petrol prices to fall before Xmas: ACCC

Motorists in Australia's biggest cities can expect to be paying less for petrol in the lead-up to Christmas.

The Australian Competition and Consumer Commission says prices have already peaked in many capital cities, meaning they should fall while demand ramps up before December 25.

"It is also important to note that as prices fall, the petrol retailers will move prices at different times, so it will pay to shop around," commission chairman Rod Sims said in a statement on Friday.

An analysis by the competition watchdog found that demand for petrol is higher in the weeks leading up to Christmas but falls significantly afterwards.

Sales then pick up in late January.

Petrol prices peaked in Sydney, Adelaide and Brisbane in recent weeks so there should not be an increase in those cities again before Christmas, Mr Sims said.

Prices in Melbourne have been falling slowly, while those in Perth will likely have to wait until next Monday to be at their cheapest.

The ACCC is encouraging drivers to use fuel price apps - such as MotorMouth, FuelCheck, NRMA and GasBuddy - to help them decide where to buy petrol.