Is E10 Actually Cheaper? What the Data Shows About Fuel Grades in Australia

Data sourced from our national fuel price database · July 2026

Have you ever wondered if E10 fuel is worth switching to? The short answer is 'it depends'. In particular, it depends on what fuel grade you're coming from. We pulled price data from over 3,000 Australian service stations to find out what the numbers actually say.

What Do the RON Numbers Mean?

Every fuel grade carries a RON (Research Octane Number) rating. Most people assume that the higher the RON rating, the more 'powerful' or energy-dense the fuel.

However, octane rating isn't about energy at all — it actually measures a fuel's ability to resist premature, uncontrolled burning (known as 'engine knock' or 'premature detonation') inside an engine's cylinder. A higher RON number means the fuel can withstand higher compression without igniting, which makes it preferable for high-compression or turbocharged engines.

E10 has a higher RON rating than U91 but costs less. That's because ethanol is cheap to blend in and improves octane chemistry, even though it has lower energy content per litre than petrol.

The Price Gap: What Bill Hero's Fuel Price Data Shows

We analysed current prices from more than 3,000 fuel stations across NSW, VIC, QLD, SA, ACT and WA. Here's the national median by fuel grade:

The E10 vs U91 price gap is remarkably consistent across all the major brands. For 7-Eleven, Ampol, BP, Caltex, Shell and United, the price premium for U91 over E10 is almost always exactly 2 cents per litre. That kind of widespread pricing discipline has to be deliberate rather than market-driven.

The Problem With E10 vs U91: Fuel Economy

Ethanol contains roughly 66% of the energy of petrol by volume. E10 is a 10% ethanol blend, which means it carries about 3.3% less energy per litre than U91.

The energy of petrol and ethanol is measured by determining their heat of combustion in a specialised and wonderfully-named laboratory instrument - the bomb calorimeter, which precisely measures the amount of thermal energy released when a specific amount of fuel is burned.

A precisely weighed mass of the fuel (petrol or ethanol) is placed in a sealed steel container (the 'bomb'), which is then filled with pure oxygen. The fuel is electrically ignited inside the bomb. It burns completely, releasing heat energy. The heat is transferred to a known volume of water surrounding the bomb, and the temperature change in the water is precisely measured.

The results are expressed in megajoules (MJ) per litre of fuel. Petrol contains about 32.2 MJ per litre, and ethanol contains about 21.4 MJ per litre.

E10 petrol, with its 90% petrol and 10% ethanol blend, works out to (0.9 x 32.2) + (0.1 x 21.4) = 31.12 MJ/l — a 3.35% reduction in MJ, which means losing the energy value of about 1 litre in every 30 litres of petrol .

If you're driving the same car on the same route, your fuel economy with E10 will be approximately 3.3% worse than on U91.

The numbers at the bowser:

Run the maths and E10's 2 c/L price advantage turns into a 2.5 c/L effective disadvantage once the 3.3% energy penalty is factored in. You'll need to buy more E10 to go the same distance.

The bottom line is that switching from U91 to E10 saves you nothing and likely costs slightly more.

Where E10 Does Make Sense: Switching From Premium

The calculus changes completely if you're currently running U95 or U98 in a car that doesn't require it. The savings there are substantial.

Based on a typical Australian driver — 50L tank, 15,000km/year, 10L/100km average consumption:

Even accounting for E10's 3% fuel economy penalty, switching from U98 to E10 saves around $330/year in real terms. Switching from U98 to U91 saves a similar amount without the economy penalty.

The State-by-State Picture

The E10 vs U91 gap varies by state:

WA is an outlier: E10 is actually 20 c/L more expensive than U91 in our current data. This reflects WA's limited E10 supply infrastructure — low volume, fewer stations stocking it, and no price competition. If you're in WA, E10 is almost certainly not the answer.

South Australia stands out the other way: the 9 c/L gap between E10 and U91 is large enough that, even with the fuel economy penalty, E10 has a marginal real-world saving.

What Fuel Does Your Car Actually Need?

This is the question worth asking before you touch anything at the bowser. Check your fuel filler cap or owner's manual. It will say one of:

• "Unleaded 91 minimum" — U91 or E10 is fine. E10 won't hurt, but won't save you money vs U91.
• "Premium unleaded 95 minimum" — U95, U98, or E10 (remember, E10's RON 94 is close enough for most engines in this category — check your manual specifically).
• "Premium unleaded 98 minimum" or "Super unleaded required" — your engine genuinely needs 98. Don't use E10.
• "E10 compatible" — explicitly cleared for E10.

Some older vehicles (pre-2010s with rubber fuel system components) should avoid E10. Motorcycles and small engines (lawnmowers, generators) are often E10-incompatible. When in doubt, check.

The Real Money-Saving Move

The E10 vs U91 debate is largely a distraction. The actual savings opportunity is:

1. If you're running U95 or U98 in a car that only needs 91 — switch to U91. You're burning ~$250/year for no benefit.
2. If your car needs 91 minimum, E10 and U91 are functionally equivalent on total cost. Don't stress either way.
3. If you're in WA, avoid E10 at current prices — it's more expensive than U91.
4. Timing matters more than grade for most drivers. Buying on Tuesday/Wednesday before the Thursday price cycle spike saves more per fill than any grade switch.

Bill Hero tracks fuel prices in real time. Check what's available near you before you fill up.