Cheapest Petrol Is a Timing Problem, Not a Brand Problem

Finding: the cheapest petrol in a city is rarely a matter of which brand you choose. It is a matter of when you buy and which station is cheapest at that moment, and both change faster than any ranking can be published. A list of “the ten cheapest fuel companies” is out of date on the day it is written, because the sites at the bottom of the price board rotate.

The more useful question is how a driver finds the low price on a given day, and how much effort the search is worth. The answer has three parts: how prices behave, which tools report them, and where chasing a cheaper price stops paying for itself.

Why a brand ranking does not hold

Fuel is priced by the individual station, not by the company. Two outlets under the same banner a few suburbs apart can show different prices on the same morning, and the difference reflects local competition more than brand policy. Independent and small-chain operators sometimes sit at the bottom of a price board, and they sometimes do not. A ranking that names brands is describing a moment, and the moment ends.

There is a second problem. A ranking has to pick a measure, such as the lowest price recorded, the average over a week, or the number of times a brand appears in a “cheap” list, and each measure reorders the table. Without the method on display, the ranking is a claim with nothing under it.

The price cycle

The Australian Competition and Consumer Commission (ACCC) monitors retail petrol prices and has described how prices in the larger cities move in cycles: a sharp rise, followed by a slower fall back down, repeated. The length of the cycle varies by city and over time: in 2025 the ACCC put the average at about one week in Perth and about six and a half weeks in Brisbane. Cycles occur in the five largest cities, not in smaller cities or most regional locations.

Two consequences follow from that pattern:

1. A fixed “cheapest day” is unreliable. The low point of the cycle moves, so advice to fill up on a particular weekday works only until the cycle shifts. Treat it as a tendency, not a rule.
2. The gap between the top and the bottom of the cycle is where the saving is. Filling up at the low point and not at the high one saves more than switching brand.

The practical response is to watch the price for a few weeks using the tools below, or to use the ACCC’s petrol buying tips for the five largest cities, which it updates three times a week. Either way, you are looking for when the price falls. Where the cycle is short, you may see the pattern yourself before you need anyone to explain it.

A worked example, using made-up numbers

Take a hypothetical driver with a 50-litre tank, and suppose the price in their area swings by 20 cents a litre between the high and low of the cycle. Filling a tank at the low point instead of the high point saves 50 times 0.20, which is $10. That is real money over a year of fill-ups, and it does not require driving anywhere unusual.

Now add the cost of chasing a better price. If the cheapest station is a ten-kilometre round trip away and the car uses, say, 8 litres per 100 kilometres, the detour burns about 0.8 litres. At a price of, say, $1.90 a litre, that is about $1.52 of fuel, before counting your time. The $10 saving still wins, but the margin is smaller than it looked.

Both figures here are illustrative. They are not current prices or any particular car’s consumption, and they leave out wear on the vehicle and the value of your time. The point of the example is the shape of the sum: savings per litre times litres bought, minus the cost of the extra distance. Run it with your own numbers before you cross town.

The tools, and what each leaves out

Government price data and the apps built on it. Several states require service stations to report prices, and the data feeds public tools. Western Australia’s FuelWatch is the long-running example, and other states run schemes of their own. Your state government’s website will say which applies to you. These tools tend to be the most current and complete. They exclude loyalty discounts, which are applied at the pump after the posted price.

Motoring club fuel finders. Many clubs offer price tools to members and sometimes to the public. They add map and route features. They may rely on the same underlying data, so check how recent each price is.

Retailer and loyalty apps. A retailer’s own app can reduce the price at its stations through vouchers or price locks. They exclude other stations, so a discount can make one outlet cheaper than a rival without making it the cheapest nearby. Check the discounted price against the open market, not against the same retailer’s own posted price.

The price board itself. Free and immediate. It excludes everything you cannot see from the road, which is why a quick look at a live tool before leaving home beats driving past boards.

A routine that works without much effort

1. Pick one live price tool and use it for a few weeks before deciding anything. Note the lowest price near your home and work, and the time it appeared.
2. Fill up when the price near you is near the bottom of what you have seen, not when the gauge is on empty. This single habit matters more than any station choice.
3. Compare any loyalty discount against the best open price before relying on it.
4. Do the detour sum before you drive more than a few minutes out of your way.

Fair limits to the advice

Cycle timing helps most for people who can choose when to fill. A driver who only has time at the end of a long day, or who runs close to empty, cannot always wait for the low point, and that is a reasonable constraint. Tank size matters too. A small tank saves less per fill. For those drivers the saving comes from picking a cheaper station among the ones they already pass.

Prices also respond to events beyond any cycle, such as changes in the wholesale price, so the low point of one week can sit above the high point of another. What stays useful is the method, not the number.

Lower the amount you buy, too

The cheapest litre is the one you do not burn. Correct tyre pressure and smooth driving reduce fuel use, and tyre care that pays you back covers the pressure side. If you are away from home and renting a car, car hire extras that cost more than the daily rate is worth reading for the fuel policy details, since returning a car with the wrong amount in the tank can cancel out any careful buying.

What this comes to

Stop looking for the cheapest brand. Look for the cheapest station today, fill up when your area’s price is low, and run the detour sum before driving far for a few cents.

Sources: Australian Competition and Consumer Commission, petrol price monitoring and price cycle information (https://www.accc.gov.au/consumers/petrol-and-fuel/petrol-price-cycles-in-the-5-largest-cities); Government of Western Australia, FuelWatch (https://www.fuelwatch.wa.gov.au); your state or territory government’s fuel price reporting information (varies by state; no single national page).