How to save big bucks filling your petrol tank

Make no mistake, the electric-vehicle revolution is coming, and there will be a time - and soon - in which we measure the cost of filling a car not in price-per-litre but in cost-per-kilowatt, and in which we'll be talking battery storage over fuel tank capacity.

But despite what that real life Iron Man, Elon Musk, might have you believe, that time is not now, and so we're still left to deal with the dark web of petrol prices. It's a weird and worrying world in which pricing can seemingly change up or down on a whim, with different days - and even different times of day - resulting in a massively different cost to fill your tank.

But there is method to this seeming madness, and if you know what to look for, and when, you can save serious dollars when it comes to filling your tank. In fact, the Australian Competition and Consumer Commission (ACCC) has been tracking 'fuel cycles' nationally - the regular patterns in which fuel prices go up and down - and it has made some interesting discoveries.

In Sydney, prices have bumped from a high of around $1.27 per litre to a low of $1.07 per litre.

In 2017, these low-high-low cycles have spanned as little as 14 days, or as long as 61 days, but there is serious money to be saved. In Sydney, for example, prices have bumped from a high of around $1.27 per litre to a low of $1.07 per litre - and everywhere in between - in the six weeks from June 15 to July 29. And so, the cost to fill an average 50-litre tank would have jumped by as much as $10 over that same period.

So, what are these cycles, and what causes them? We'll let fuel-tracking firm, Motor Mouth explain.

“What happens is everyone shuffles their prices to try and maintain that competitive advantage, and it gets to a stage where it becomes uneconomical, because retailers are selling fuel below cost, so the market then corrects itself before it starts all over again," Motor Mouth's regional manager, Asia-Pacific, Chris Huth, told CarsGuide.

“Retailers chase each other to the bottom, and then the cycle starts all over again," he said.

In keeping on top of these cycles, technology is your friend, and your first port of call should be the ACCC's petrol price guide, an awesome resource that is updated daily and gives you access to real-time and historical data detailing where we are in a petrol cycle, and even tips on whether you should fill your tank now, or wait until prices drop.

Local legislation demands petrol retailers publish the next day's prices every evening.

Your location is important, too. In Perth, the cycles tend to run like clockwork, meaning the best time to buy petrol is a Monday, with prices peaking on a Tuesday, then gradually falling over the course of the week.

That's because local legislation demands petrol retailers publish the next day's prices every evening, limiting the amount of fluctuation. In the other states and territories, though, it's not so cut and dried, with prices fluctuating according to the fuel cycle and not days of the week.

Wherever you live, though, there are services set up to help you find a fuel bargain, with websites and apps that will compare fuel prices, and even offer a 'cheap fuel near me' function.

The NSW state government's Fuel Check site is a simple-to-use tool that will give you the average cost-per-litre across the state, and display an interactive map offering real-time price data for the petrol stations in your area.

Alternatively, Motor Mouth offers a national service, and can be downloaded as an app on your phone. Fuel price cycle and cost-per-litre information is updated as often as every 15 minutes, giving you real-time advice on when to fill your tank.

“Once upon a time it was a fairly regular seven-day cycle, where every Tuesday or Wednesday was the cheap day, but now it's more important to use tools to track where this cycle is, as they are much longer than seven days now," Mr Huth says.

“If the cycle is high, top up. If the cycle is low, fill up," he adds.

Do you have a tricky method for buying fuel at the best price? Tell us about it in the comments below.