Perth motorists who buy petrol at the low point of the regular price cycle can save up to $520 per year, a new ACCC report has revealed.

The report found it has become easier in Perth to pick the "trough" and "peak" days of price cycles, while it is getting harder to do so in the eastern states.

Price cycles involve sudden increases in petrol prices, usually led by one or more retail sites. The decline back to lower price levels is slower than the increase.

The advice is not to wait until your tank is nearly empty to fill up. Credit:Greg Newington

“While they are not illegal, the retailers’ use of price cycles to maximise profits really infuriates drivers as they can see no reason for them to exist,” ACCC Commissioner Mick Keogh said.