E10 vs Unleaded 91: Which Fuel Should You Use?

Every time you pull up to a servo you face the same little decision: E10 or Unleaded 91? E10 almost always sits a few cents a litre cheaper, so it looks like the obvious pick. But the cheaper sticker price hides a catch - E10 carries slightly less energy, so your car burns a touch more of it. Once you account for that, the "cheaper" fuel isn't always cheaper to drive on.

This guide breaks down exactly what E10 is, how much you really save (with the maths), which cars can and can't use it, and a simple rule of thumb for the bowser. And if you just want today's cheapest E10 and 91 near you, you can compare both live on the Fuel Daddy fuel map - free, no sign-up.

What exactly is E10?

E10 is regular unleaded petrol blended with up to 10 per cent ethanol. The ethanol is made from plant sources - in Australia that's mostly sugarcane and grain - which makes E10 a partially renewable fuel. Despite the lower price, it carries a minimum octane rating of 94 RON, which is actually higher than standard Unleaded 91.

Unleaded 91 (ULP 91) is the baseline petrol grade in this country. It contains no ethanol and rates 91 RON. It's been the default fuel for Australian cars for decades and runs in virtually every petrol engine on the road. If you've never thought about which fuel you put in, you've almost certainly been buying 91 by default.

Octane (the RON number) measures a fuel's resistance to knocking, not how much "power" it holds. A higher number doesn't automatically mean a better fuel for your car - it just means the fuel suits engines designed for it. For most cars that call for 91, E10's higher 94 rating is harmless and occasionally a small bonus. If you want the full octane rundown, our premium vs regular petrol guide goes deeper.

How much do you actually save with E10?

Across most Australian markets, E10 typically prices 2 to 5 cents a litre below Unleaded 91. On a 50-litre fill that's a $1 to $2.50 saving at the bowser. Over a year of fortnightly fills, that's roughly $25 to $65 in raw pump savings - which sounds like an easy win until you read the next paragraph.

Here's the catch. Ethanol holds about 34 per cent less energy per litre than pure petrol. In a 10 per cent blend, that works out to roughly 3 per cent less energy overall. So your engine has to burn a bit more E10 to do the same work. Most drivers see fuel economy drop by about 1 to 3 per cent on E10 compared with 91. That extra consumption quietly eats into the price saving.

The table below shows how it plays out over a typical year. The numbers assume 15,000 km, a car using 8.0 L/100 km on Unleaded 91, and a 3 per cent economy penalty on E10.

That's the surprise most people miss. At a 4-cent gap the two fuels land almost dead level per kilometre. So the real driver of value is the size of the price gap on the day, not the fact that E10 is cheaper on the board. Here's the simple rule that falls out of the maths:

• Gap of 4 c/L or more - E10 usually wins on cost per kilometre.
• Gap of 2 c/L or less - Unleaded 91 can actually be cheaper to drive on.
• Gap of around 3 c/L - line ball; pick either.

To run these numbers for your own car and weekly distance, plug them into the Fuel Daddy fuel cost calculator. And before you fill up, check the actual gap at stations near you on the live fuel map - that gap moves day to day, so the better fuel changes too.

Can your car use E10?

The vast majority of petrol cars built from 2005 onwards are designed to run E10 with no issues at all. That covers most Toyota, Mazda, Hyundai, Kia, Ford, Holden and similar models sold here. If your car was built this side of 2005, it's very likely E10-compatible - but it pays to confirm rather than assume.

The quickest checks: look inside the fuel filler flap for an E10-compatible sticker, or check your owner's manual. Many cars also list approved fuels on a label near the cap. If it says "Unleaded 91 only" or "no ethanol blends", take that at its word. Running E10 in an engine that isn't rated for it can, over time, degrade older rubber seals and fuel-system components.

Vehicles that should avoid E10

Some vehicles and engines should stick with straight Unleaded 91 (or whatever the maker specifies):

• Cars built before 2005 - check the specific model before assuming.
• Some older European models, particularly certain BMW, Mercedes-Benz and Volkswagen vehicles.
• Many motorcycles, boats, and small engines - mowers, chainsaws, generators.
• Anything where the maker explicitly states "no ethanol blends".
• Classic and collector cars with original rubber fuel-system parts.

If you drive a modern hatch or SUV around Brisbane, the Gold Coast, Sydney or Newcastle, E10 will almost certainly be fine. Browse every suburb in your state on the Queensland locations hub or the New South Wales locations hub to see live E10 and 91 prices near you.

Does E10 affect performance or engine health?

For a compatible engine, E10 causes no performance problems in normal driving. Because it rates 94 RON against 91's lower number, some modern engines with knock sensors can pull marginally better performance from it - though the difference is so small you won't feel it on the commute. For everyday driving, an E10-rated car runs exactly as it would on 91.

The one genuine quirk is storage. Ethanol is hygroscopic, meaning it draws moisture out of the air. If E10 sits in a tank for months on end, it can absorb water and risk corrosion or hard starting. That matters for seasonal vehicles, boats, and cars that sit idle for long stretches - not for anything you drive every week. If your car gets regular use, this simply isn't a concern.

This is also why small equipment makers often warn against E10: a mower or generator that sits in the shed for half the year is exactly the case where moisture absorption bites. Fuel that turns over quickly never sits long enough to be a problem.

When does E10 make sense, and when doesn't it?

Put the two together and the decision is straightforward. E10 is the better pick when your car is confirmed compatible, the price gap is 4 c/L or more, and you drive regularly enough that fuel never sits for months. On those days, you're saving real money per kilometre and supporting a partly renewable fuel.

Stick with Unleaded 91 when any of these apply:

• Your car isn't approved for ethanol blends.
• The price gap is under 3 c/L - the economy penalty erases the saving.
• You're filling equipment that sits unused for weeks or months.
• Your manufacturer specifically recommends non-ethanol fuel.

Choosing the right grade is one lever. Timing your fill is another, and it's often the bigger one. Our guide on the best time to buy fuel shows how the price cycle works, and the save money on fuel guide stacks every trick together. Use a supermarket loyalty docket on top and the savings compound.

Finding the cheapest E10 and 91 near you

Pump prices swing hard between stations, even within the same suburb. On any given day you might find E10 at 169.9 c/L at one site and 179.9 c/L two kilometres up the road. That 10-cent spread dwarfs the 3-to-5-cent gap between E10 and 91 - which is why finding the cheapest station matters far more than agonising over the grade.

That's the whole point of the live Fuel Daddy map: pull up E10 and 91 prices side by side at every station near you, then drive to the cheapest one you'll actually pass. Prices update through the day from the official QLD and NSW fuel-reporting schemes.

One more angle worth a look if you're weighing up your next car: running costs differ a lot by fuel type. Our diesel vs petrol running costs comparison and, for the electric-curious, our EV charging cost vs petrol breakdown both put real numbers on it. And if a Costco station is on your route, its everyday E10 and 91 prices are often the cheapest going - track them on the Costco fuel prices hub or read our full Costco fuel guide.

The bottom line

E10 is a fine, often slightly cheaper fuel for any car that's rated for it - which is most cars built since 2005. But the saving is smaller than the board suggests, because E10's lower energy means you burn a little more of it. The honest rule: take E10 when the price gap is 4 c/L or more and your car is compatible; stick with 91 when the gap is thin, your car isn't approved, or you're filling something that sits idle.

Either way, the biggest saving isn't the grade - it's the station. Compare E10 and 91 at every servo near you, today, on the live fuel map.