TL;DR: With Brisbane fuel at record highs, I converted today’s board medians to what each grade actually costs to drive per 100km — and the pump price lies. If your car takes 91, run 91: it’s $17.92/100km, and E10, 95 and 98 all cost more to drive. E10 is the trap — it’s 2c/L cheaper at the bowser (236.9 vs 238.9) but about 40c/100km dearer to drive, because its ~3% economy penalty outweighs the discount. And in the drivetrain contest, diesel still edges it at $17.39/100km — the cheapest of all five despite the highest pump price (289.9 vs 91’s 238.9) — because 6.0 vs 7.5 L/100km beats the 51c/L premium. But that edge is the thinnest it’s been: break-even is a 59.7c premium, diesel’s at 51c, so only ~8.7c of headroom, and diesel’s been climbing hardest. The biggest lever isn’t the grade at all — it’s which servo. The 91 spread today is ~21c/L (cheapest 217.5 vs median 238.9), bigger than any gap between grades.
The question
Prices are at record highs, the board is full of numbers, and every one of them is in cents-per-litre. That’s the wrong unit. The litre isn’t what you’re buying — the kilometre is. A grade that’s cheaper at the pump can be dearer to drive, and a grade that’s dearer at the pump can be cheaper to drive. The only fair question at these prices is: what does each grade actually cost to move the car 100km?
So I ran all five — 91, E10, 95, 98, diesel — through cents-per-100km on today’s Brisbane medians.
What I checked
Every price here is the Queensland Government feed — the board price each station reported, not a driver’s guess at the pump. Same feed that fills the map. Today’s medians, 27 September, across Brisbane metro:
- 91: 238.9c/L
- E10: 236.9c/L (2c/L under 91)
- 95: 255.9c/L
- 98: 263.9c/L
- Diesel: 289.9c/L (51c/L over 91 — the highest board price of the lot)
To turn cents-per-litre into cents-per-100km you need how many litres each grade burns per 100km, and that’s where the pump price stops telling the whole story. I used the same economy assumptions as the companion posts, so the numbers line up across the blog:
- Petrol at 7.5 L/100km, diesel at 6.0 — the standard 20% diesel economy edge from the diesel running-cost post.
- E10 carries a ~3% economy penalty (ten per cent ethanol, less energy per litre) — the figure from the E10 post.
- 95 and 98 in a 91-tuned car get a ~2% economy credit — the figure from the premium-petrol post.
Those percentages are external published guidance, not our price data — I’ll flag them hard in the limits, because they’re the lever the whole sum turns on. The c/L prices are exact from the feed.
What the data shows
Run every grade through its own economy figure and the ranking flips against the board:
Two separate stories are hiding in that chart, and it matters not to blur them.
Finding 1 — the same-car petrol choice: run 91
If your car takes 91, all four petrol options are yours to choose between, and 91 is the cheapest to drive:
- 91: 238.9 × 7.5 = $17.92/100km
- E10: 236.9 × 7.5 × 1.03 = $18.30/100km
- 95: 255.9 × 7.5 × 0.98 = $18.81/100km
- 98: 263.9 × 7.5 × 0.98 = $19.40/100km
E10 is the sting in the tail. It’s the cheapest on the board — 2c/L under 91 — and it’s the second-dearest to drive of the four, about 40c/100km more than 91. The 2c/L you save at the pump is worth about 15c/100km; the ~3% economy penalty costs about 55c/100km. Net, you lose. “E10 is the cheap fuel” is the pump price lying to you — the discount is real, the kilometres it buys aren’t.
95 and 98 lose too, and by more: even after crediting the 2% economy gain a 91-tuned engine can realise, 95 costs about 89c/100km more than 91 and 98 about $1.48 more. On a car that only needs 91, the premium buttons are money for nothing — the premium-petrol post has the full teardown, but at record prices the loss is just bigger.
The exception is the same one it always is: if your handbook requires 95 or 98, this doesn’t apply — pay the gap, that’s where premium earns its keep.
Finding 2 — the drivetrain contest: diesel still edges it, barely
This one comes with a warning label, because it’s easy to read the chart wrong. You can’t put diesel in a petrol car. Finding 1 is a choice you make at the pump this morning; Finding 2 is a choice you made when you bought the car. They’re not the same decision, and diesel isn’t a fifth button on your 91 car’s bowser.
But if you’re weighing a petrol car against a diesel one — or you already own the diesel and want to know if it’s still paying off — the maths says diesel still wins per 100km, even at $2.90:
- Petrol (91): $17.92/100km
- Diesel: 289.9 × 6.0 = $17.39/100km
Diesel comes out about 53c/100km cheaper, despite costing 51c/L more at the bowser, because the 20% economy edge (6.0 vs 7.5 L/100km) more than covers the premium. The board says diesel is the dearest fuel in Brisbane; the kilometre says it’s the cheapest.
The catch is how thin that edge has become. With a 20% economy advantage, diesel wins until its premium tops 0.25 × the petrol price — that’s the break-even from the diesel post. At today’s 238.9c petrol, break-even is a 59.7c/L premium. The actual premium is 51c. So there’s only about 8.7c/L of headroom left before diesel loses its per-kilometre advantage entirely. And diesel’s been the grade climbing hardest into these record highs — a few more cents on the premium and the edge is gone. Diesel’s still ahead, but it’s the thinnest margin it’s been.
The verdict
At record prices the ranking on the board is not the ranking that matters. Per 100km, diesel is cheapest (in a diesel car), then 91, then E10, then 95, then 98. The cheapest board price (E10) is the fourth-cheapest to drive; the dearest board price (diesel) is the cheapest to drive. Cents-per-litre is a decoy — every grade goes a different distance on a litre, so only cents-per-100km settles it.
So what for you
Three honest takeaways:
- If your car takes 91, run 91. Skip E10, skip 95, skip 98 — all three cost more to drive than plain 91 at today’s prices, and E10’s “cheap” board price is the biggest trap of the three.
- If you’re choosing or already own a diesel, it’s still marginally cheaper to run — about 53c/100km — but the edge is the thinnest it’s been (8.7c of headroom), and it’s shrinking as diesel climbs. Don’t buy a diesel for the fuel saving at these prices; if you already have one, it’s still just ahead.
- The biggest lever is which servo, not which grade. The 91 spread across Brisbane today is about 21c/L — cheapest 217.5c against the 238.9c median — bigger than the gap between any two grades in this post. Picking the right station beats picking the right grade, every time.
You can see today’s cheapest near you on Pinly Fuel, straight off the Queensland Government feed, so the number on the map is the number at the pump.
How we measure: Brisbane-metro median board prices from the QLD Government feed, 27 September 2026 — 91 at 238.9c/L, E10 236.9, 95 255.9, 98 263.9, diesel 289.9, and the cheapest 91 at 217.5. Every price traces to that snapshot. The cents-per-100km conversions lean on economy assumptions that are external published guidance, not our feed: 7.5 L/100km petrol and 6.0 diesel (a 20% edge), a ~3% E10 economy penalty, and a ~2% premium-petrol credit on a 91-tuned engine. Those percentages are the biggest lever in the sum and they vary by car and by city-vs-highway driving, so plug in your own real figures before you trust the verdict — the diesel edge in particular sits inside its 8.7c/L break-even headroom, so a smaller real-world economy advantage or a few more cents of premium flips it. This is running cost only — no purchase price, servicing or AdBlue. And none of this is engineering advice: if your manual requires a specific grade, that trumps every number here.
— Nate