Can I mix different fuel types?

You can mix different octane levels of petrol (e.g., 91 and 95) without damaging your engine — the result is simply an intermediate octane rating. However, you should never mix petrol and diesel. Putting diesel in a petrol car or petrol in a diesel car can cause serious engine damage and requires the tank to be drained immediately.

Is premium fuel worth the extra cost?

Only if your car is designed for it. Cars that require 95 or 98 octane have higher-compression engines that benefit from the increased knock resistance. For these vehicles, premium fuel delivers better performance and can actually improve fuel economy. But if your car is designed for 91, premium fuel provides no measurable benefit — you're just paying more.

What happens if I use the wrong fuel?

Using a lower octane than recommended can cause engine knocking, reduced performance, and potential long-term damage. Using a higher octane than required is safe but wasteful. The most dangerous mistake is putting petrol in a diesel car or vice versa — this requires immediate professional draining before starting the engine. If you've misfuelled, do not start the car; call roadside assistance.

Fuel Types Explained: Which One Does Your Car Need?

Walking up to a fuel bowser and seeing five or six different nozzles can be confusing. Unleaded, premium, E10, diesel — what's the difference, and does it actually matter which one you choose? The short answer: yes, it matters. Using the wrong fuel can cost you money, reduce performance, or even damage your engine. Here's a plain-English guide to every common fuel type.

Unleaded 91 (Regular)

Unleaded 91 is the standard petrol grade and the cheapest option at the bowser. The "91" refers to its Research Octane Number (RON), which measures the fuel's resistance to engine knocking. Most everyday cars — sedans, hatchbacks, and older models — are designed to run perfectly on Unleaded 91. If your owner's manual says 91 RON, there's no benefit to paying extra for premium.

Check current Unleaded 91 prices in Australia or New Zealand.

Unleaded 95 (Premium)

Unleaded 95 is a mid-grade premium fuel with a higher octane rating. Many modern cars, particularly European imports and turbocharged engines, are designed to run on 95 RON. For these vehicles, using 95 delivers the performance and fuel economy the manufacturer intended. Using 91 in a car that requires 95 can cause engine knocking and reduced performance, and may void your warranty.

If your car only requires 91 but recommends 95, you'll see a marginal performance improvement that rarely justifies the price difference. Check current Unleaded 95 prices.

Unleaded 98 (Super Premium)

Unleaded 98 is the highest-octane petrol widely available. It's designed for high-performance and turbocharged engines that generate higher compression ratios and temperatures. Sports cars, performance sedans, and many European vehicles specify 98 RON for optimal output. These engines can extract more power and better efficiency from the higher octane rating.

For cars that only require 91 or 95, filling with 98 is simply a waste of money — your engine can't take advantage of the higher knock resistance. Compare Unleaded 98 prices near you.

E10 (Ethanol Blend)

E10 is a blend of 90% unleaded petrol and 10% ethanol, a renewable fuel made from plant materials like sugarcane or corn. It's typically 3-5 cents per litre cheaper than Unleaded 91, making it an attractive option for budget-conscious drivers. Most cars manufactured after 2005 are compatible with E10 — check your owner's manual or the fuel flap for confirmation.

The trade-off is that ethanol contains about 30% less energy per litre than pure petrol, so you'll use roughly 3% more fuel. For most drivers, the lower price still makes E10 the cheaper choice per kilometre. Check E10 prices to compare.

E85 (Flex Fuel)

E85 contains 85% ethanol and 15% petrol. It's significantly cheaper per litre but delivers roughly 25-30% fewer kilometres per tank due to ethanol's lower energy content. E85 is only suitable for flex-fuel vehicles (FFVs) specifically designed to handle high ethanol blends — using it in a standard car will cause serious engine damage.

E85 is most common in Brazil, where sugarcane ethanol is widely produced, and in parts of the United States. In Australia, availability is limited to select stations. If you drive a flex-fuel vehicle, E85 can offer significant savings despite the reduced range.

Diesel

Diesel fuel is fundamentally different from petrol — it's ignited by compression rather than a spark plug. Diesel engines are known for strong low-end torque, better fuel economy (often 20-30% better than equivalent petrol engines), and longer engine life. They're the standard choice for SUVs, utes, trucks, and vehicles used for towing or long-distance driving.

Diesel is sometimes priced higher than petrol per litre, but the superior fuel economy often makes it cheaper per kilometre. Never put petrol in a diesel car or diesel in a petrol car — this is the most common and expensive misfuelling mistake. Check current Diesel prices in Australia or Diesel prices in the UK.

LPG / Autogas

LPG (Liquefied Petroleum Gas) is the cheapest fuel per litre, typically costing around half the price of unleaded petrol. However, LPG has about 25% less energy per litre, so your car will use more of it. Even accounting for the reduced economy, LPG usually works out 30-40% cheaper per kilometre than petrol.

The catch is that your car needs an LPG conversion kit (costing $2,000-$4,000), and the number of LPG stations has been declining in some markets. LPG makes most financial sense for high-mileage drivers — taxis, rideshare drivers, and long-commute workers — who can recoup the conversion cost within a year or two.

How to Find Your Car's Required Fuel Type

The easiest way to check is the fuel flap on your car — most manufacturers print the minimum octane requirement there. Alternatively, check your owner's manual or search your car's make and model online. Using the correct fuel type ensures your engine runs efficiently, maintains its warranty, and avoids unnecessary costs. For tips on reducing your overall fuel spend, see our guide to saving money on fuel.