The car we used
A medium petrol car using 8 litres per 100 kilometres, driven 250 kilometres a week, which is 13,000 kilometres a year and about 1,040 litres. At $2.50 a litre that is $2,600 a year on fuel. Put your own car into the fuel cost calculator to scale these numbers to you.
| Habit | Saving a year |
|---|---|
| Buying at the right point in the price cycle | $150–$260 |
| Easing off from 110 to 100 km/h on highway trips | up to $100 |
| Not buying premium when your car is designed for 91 | $100–$200 |
| Using a 4c docket every fill | about $40 |
| Choosing E10 over 91 at a 3c discount | about −$55 |
Our estimates for the example car, explained below. A negative saving means it costs you money.
1. Buy at the right point in the price cycle
In Sydney, Melbourne, Brisbane, Adelaide and Perth, unleaded moves in a cycle of a sharp jump followed by a slow slide. The difference between the top and the bottom is often 20 to 30c a litre or more. You will not hit the bottom every time, but if you avoid filling up in the few days after a jump and save the full tank for when the margin is low, an average saving of 15 to 25c a litre is realistic.
On 1,040 litres a year, 15 to 25c a litre is $150 to $260. It is the biggest saving available and it costs nothing but attention.
The easy way to judge it is to compare the price on the sign with the wholesale price for your city on our city pages. Within 10c of wholesale is a good day. More than 25c over is a bad one.
2. Check tomorrow's price where you can
In Western Australia and Victoria, servos publish tomorrow's price, or price cap, the afternoon before, and cannot raise it during the day. If tomorrow is dearer, fill up today. In Perth, where the cycle is weekly, that alone captures most of the cycle saving above. Our guide to the state apps lists the official service for each state.
3. Ease off on the highway
Air resistance rises with the square of speed, so at 110 km/h a car pushes through about 21% more drag than at 100 km/h. At highway speeds drag is roughly half the work the engine does, which is why most cars use something like 10% more fuel at 110 than at 100. If a third of your driving is highway driving at 110, easing off to 100 saves about 3% of your fuel, roughly $80 to $100 a year, and costs a few minutes on a long trip.
4. Use the grade your car needs, not a better one
Premium 95 or 98 usually costs well over 10c a litre more than 91. If your car is designed for 91, it cannot make meaningful use of the extra octane, so paying 10 to 20c a litre more costs $100 to $200 a year for little in return. If your car is designed for premium, use premium, because any saving from 91 would be lost to lower economy. The E10 and premium guide has the detail.
5. Use discount dockets, but don't chase them
A 4c docket on a 50-litre fill is worth $2. Used on most fills, about $40 a year. That is worth having, but it comes off whatever the servo chooses to charge. A docket at a servo 15c above the one across the road is a loss of 11c a litre. Use dockets at the bottom of the cycle, not instead of it.
6. Don't assume E10 is cheaper
E10 contains about 3% less energy than regular unleaded, so most cars use about 3% more of it. At $2.50 a litre, E10 has to be at least 7c cheaper than 91 to break even. At a 3c discount, the extra 3% of fuel costs this car more than the discount saves, about $55 a year more. Worth checking for your own car with the calculator in the E10 guide.
The small things
- Tyre pressure. Under-inflated tyres increase rolling resistance. Check them monthly against the placard on the driver's door pillar. It costs nothing and helps braking and tyre life too.
- Roof racks and boxes. They add drag at highway speed. Take them off when you are not using them.
- Idling. A stationary engine uses fuel for nothing. Modern engines restart easily, so switching off for long waits makes sense.
- Smooth driving. Hard acceleration followed by hard braking turns fuel into brake heat. Looking further ahead and coasting to lights helps, especially in city driving.
What doesn't work
- Filling up early in the morning because fuel is cooler and denser. Fuel is stored underground at a near-constant temperature. The difference is negligible.
- Driving across town for a few cents. A 20-kilometre round trip costs about $4 in fuel. A 5c saving on 50 litres is $2.50.
- A fixed "cheap day" outside Perth. In the other cycling cities, the cycle is several weeks long and does not line up with the days of the week.
Where these figures come from
Wholesale prices are the terminal gate prices published each weekday by the Australian Institute of Petroleum, which we hold back to 2004. The national figure is AIP's own average where it has published one, and our weighted calculation in between, which matches AIP's to within 0.1c. Oil and currency prices are delayed market closes. Excise rates are the ATO's. We check every figure against that data before publishing and correct mistakes in the update log. Spotted one? Email hello@thepetrolprice.com.