It looks like Mandurah motorists will now have to wait a fortnight for a cheap fill-up day rather than weekly.
FuelWatch warned unleaded petrol (ULP) will now be cheapest every second Tuesday, as major petrol outlets start conforming to a fortnightly cycle.
For almost two years the weekly cycle has been consistent with most fuel outlets in Perth and Mandurah increasing ULP prices every Wednesday by about 40 cents per litre.
However, in recent weeks, major fuel companies have altered its prices to a bi-weekly cycle with price hikes due every second Wednesday.
FuelWatch manager Ben Derecki said the fuel companies have given no explanation for the change in the price cycle.
"This latest change in the cycle will make it more difficult for Perth motorists to find cheaper petrol if they fill up every week," he said.
"Previous disruptions to the cycle involved a change in the day of the week in which the price hike occurred, making it easier for consumers to adjust, but this change makes planning fill-ups more problematic."
The new cycle comes as metropolitan petrol prices recently skyrocketed, with an all-time high daily average price of 174.1 cents per litre last week.
If you're not on empty wait until next Tuesday, October 19 to fill up your tank.
Head to www.fuelwatch.wa.gov.au to find the cheapest fuel in your area on any given day.