Mount Gambier Diesel Up 17 Cents in Five Days as Every Mainland State Moves in Lockstep

Mount Gambier Diesel Up 17 Cents in Five Days as Every Mainland State Moves in Lockstep

The diesel numbers pulled at 2:06pm AEST on 19th Sep 2026 put Mount Gambier at an average of 271.2 cents a litre across six servos. That makes it the only South Australian town among the forty cheapest diesel suburbs in the country today. It is also 17.0 cents dearer than it was at the same time on Monday. Both of those things are true at once, and the second deserves closer scrutiny.

Comparing like with like

Day to day comparisons are unreliable in a week like this. Servos lodge new prices at different times, and the sites that have not yet repriced drag any figure for "yesterday" down. So I have compared the same 2pm snapshot five days apart, which puts every town and every state on the same footing.

On that basis, Mount Gambier diesel averaged 254.2 cents on Monday 14th Sep. By Thursday morning it was 261.7, and this afternoon it is 271.2. That is a rise of 17.0 cents in five days, in the one South Australian town that still makes the national cheap list.

Five states, almost the same increase

Digging deeper into the numbers, Mount Gambier turns out not to be a local story at all. Between 2pm Monday and 2pm today the NSW diesel average went from 262.8 to 283.3, up 20.5 cents across 1,180 stations. Queensland went from 264.3 to 283.8, up 19.5 cents, and Victoria from 262.3 to 281.7, up 19.4. South Australia moved from 265.4 to 283.0, up 17.6 cents across 364 stations, and Western Australia from 263.7 to 280.9, up 17.2.

These are five states with different retailers and different levels of local competition, yet the increases sit within 3.3 cents of each other. On Monday the five averages were bunched within 3.1 cents, and today they are bunched within 2.9. The whole pack has moved up together.

This raises some interesting questions about where the increase is coming from. A single suburb lifting is a local pricing decision. When five states rise by near identical amounts in the same week, the pressure is almost certainly coming from further up the supply chain, and no amount of shopping between states will dodge it.

The two territories sit above the pack. The ACT has moved further still, up 22.3 cents to 297.9. The Northern Territory remains the dearest jurisdiction at 309.5 and is the only one above 300 cents, so Territory motorists should keep the NT 24 hour price lock in mind when timing a fill.

Where the savings still are in Mount Gambier

A rising average does not mean every servo has moved equally, which is why it still pays to check the board before pulling in.

The cheapest diesel in Mount Gambier this afternoon is 262.5 cents and the dearest is 287.9. That is a 25.4 cent spread inside one regional city, worth $15.24 on a 60 litre fill. The cheapest servo in town is 20.5 cents under the South Australian average of 283.0, while the dearest is 4.9 cents above it, on the same day and for the same fuel.

The town average sits 11.8 cents under the state figure and 10.5 cents under the Victorian average just across the border. For anyone driving the Princes Highway between Adelaide and Melbourne, that makes Mount Gambier a sensible place to fill, provided you pick the right servo.

Tintinara on the Dukes Highway tells the same story on a smaller scale. Its three servos averaged 259.9 on Thursday morning and 268.9 this morning, a 9.0 cent rise in two days.

The cheap end of the national list

Outside South Australia, Pinjarra has the lowest suburb average on today's list at 260.9 across five servos, with only 3.6 cents between cheapest and dearest. Wagga Wagga averages 266.2, and Bundaberg sits at 269.7 with just 0.6 cents separating its three servos. North Geelong, which I noted on Wednesday was holding at 254.9, now averages 270.4. It did not hold for long.

What motorists should take from this

The rise is national, so there is no point waiting for your own state to fall back into line. The saving on offer sits between servos rather than between states. The gap inside a single town is now worth far more than the gap across the country: 25.4 cents inside Mount Gambier against 2.9 cents between the five mainland averages.

So check before you fill. Compare diesel prices in your suburb, look at price trends to see how far your area has already moved, and run a weekly fill through the savings calculator if you drive a ute or a work vehicle. Petrol drivers can do the same with unleaded petrol prices.

I will be watching whether the five mainland averages stay bunched this tightly through the coming week. Armed with this information, motorists in Mount Gambier and along the Princes Highway can check what their own servo is charging before they pull in.