A plain-English guide to choosing between 91, 95, 98 and E10 at the bowser, based on the minimum octane your car's manufacturer actually specifies.
Which Petrol Should I Use: 91, 95, 98 or E10?
Use the minimum octane your car's manufacturer specifies, and nothing below it. That single rule answers it for almost every driver. Open the owner's manual or look at the sticker inside the fuel filler flap: it will name the fuel the engine was built for. Most everyday cars are happy on 91 or E10. A car designed for premium will say 95 or 98, and going lower than that number is the one mistake that can actually cost you.
The octane number tells you how well the fuel resists knocking, which is uncontrolled combustion that a performance engine is tuned to avoid. It is not a quality score and it is not a power rating. Pouring 98 into a car that only asks for 91 will not make it faster, quieter or cleaner. It just empties your wallet quicker. The value is in matching the fuel to the engine, not in buying the biggest number on the bowser.
What Is the Difference Between 91, 95, 98 and E10?
The difference is the octane rating and, in the case of E10, the ethanol content. At almost any Australian servo you will find these four pump fuels. Here is how they compare.
| Fuel | Octane (RON) | Typical price | Best suited to |
|---|---|---|---|
| E10 | Around 94 | Lowest | Cars listed as E10 compatible, usually cheaper to run |
| Unleaded 91 | 91 | Low | The majority of cars on Australian roads |
| Premium 95 | 95 | Moderate | Many European cars and imports, plus mild performance engines |
| Premium 98 | 98 | Highest | Performance and turbocharged engines that specify it |
E10 is regular unleaded with up to 10% ethanol mixed in. Standard 91 has no ethanol. The jump from 91 to 95 to 98 is purely about octane, so the fuels look and pump the same, they just behave differently under load in an engine tuned to use them. Some imports are badged "Premium Unleaded Only", which means 95 or 98 is not optional for that car.
Is E10 Better Than Unleaded 91?
E10 is cheaper, not better. It sits a few cents under 91 at most stations, which is why it appeals, but the 10% ethanol carries slightly less energy than straight petrol. In practice that can mean a small drop in fuel economy, so the saving at the pump is sometimes eaten back by how far a tank takes you. Regular 91 has no ethanol and often returns marginally better mileage, especially in older or premium engines.
The bigger question is whether your car can take E10 at all. Most petrol cars built from around 2005 onwards are fine on it, but some older engines and a few specific models are not. Check the fuel flap sticker or the manual before you switch. If your car is approved for E10 and you do a lot of short suburban runs, it is a reasonable way to trim the weekly spend. If you cover long highway distances, the better economy of 91 can cancel out the price gap.
What Is the Real Difference Between 91 and 95?
The real difference is four octane points and who the fuel is for. Unleaded 91 is the standard fuel most Australian cars are designed to run on. Premium 95 has a higher octane rating that lets engines with higher compression, common in European models and mild performance cars, run the way they were tuned to. If your car specifies 95, use 95. If it specifies 91, moving up to 95 usually does nothing you can feel, and it costs more every fill.
There is one grey area. Some engines are built to run on 91 but can take advantage of higher octane through their engine management, giving a very small gain in economy or smoothness. For most drivers that gain is too small to justify the price difference over a year. The safe answer stays the same: match the minimum your maker sets, and only go higher if the manual says the car benefits.
Is Premium 98 Worth It Over 95?
Only if your car actually calls for 98. Both are premium fuels, but 98 has a higher resistance to knocking, which suits high-compression engines tuned for precision. If the manufacturer specifies 98, using 95 can pull timing and cost you performance, so pay for the 98. If the car is happy on 95, stepping up to 98 gives no meaningful benefit and simply costs more every fill. Think of it as buying champagne for someone perfectly content with a beer.
Premium fuels do carry more cleaning detergents, which is the argument you will hear for running 98 in anything. The honest version is that the extra detergent will not transform a car that only needs 91. It is a minor perk, not a reason to pay premium prices on an engine that was never built for them. Buy the octane your car requires, and let the detergent question look after itself.
How Do I Find Out What Fuel My Car Takes?
Two places tell you for certain: the sticker inside the fuel filler flap and the fuel section of the owner's manual. One of them will state the minimum octane, and often the word "minimum" is printed right there, which means you can safely go higher but never lower. That flap sticker is the quickest check when you are standing at the bowser and cannot remember. Guessing the wrong fuel can affect performance, add engine wear, and on imports and performance cars it can even void the warranty.
If you have lost the manual and the sticker has worn off, the safe default for a standard petrol car is 91. Do not guess upward assuming premium is a treat for the engine, and never guess downward on a car badged for premium. When in doubt, look the model up by its build year and engine, or ask a mechanic. Running the correct fuel is one of the cheapest things you can do to keep an engine healthy.
Does Premium Fuel Clean Your Engine?
Partly. Premium fuels, both 95 and 98, contain more detergents than standard unleaded, and those detergents help keep carbon from building up in the fuel system. So there is a grain of truth to the idea that 98 keeps an engine cleaner. The claim gets oversold, though. On a car that only needs 91, an occasional tank of 98 makes little practical difference to how clean the engine stays.
Compared with E10 or 91, premium 98 does carry extra additives aimed at cleaning injectors and reducing carbon over time. It is not magic, but with regular use it can help a little. If your real goal is a clean fuel system, a dedicated fuel system cleaner does far more than a tank of premium, and so does staying on top of servicing. Paying for 98 purely to clean an engine that runs fine on 91 is money you do not need to spend.
What Is E85 Fuel and Can I Use It?
E85 is petrol blended with up to 85% ethanol, with an octane rating above 100 RON. It is made for race cars and factory flex-fuel vehicles, not ordinary road engines. On a car tuned for it, E85 can make more power, it often costs less per litre than 98, and it burns cooler, which helps keep engine temperatures down under hard use.
For everyone else it is the wrong choice. E85 burns faster than regular petrol and the high ethanol content can attack fuel system components that were never designed for it. Unless your car is specifically flex-fuel rated or has been built to run E85, leave it at the pump. There is no economy or performance benefit to be had from pouring it into a standard engine, only the risk of damage.
How Can I Save Money on Petrol?
The fastest saving is to stop buying octane your car does not need, then time your fills to the price cycle. Fuel prices in most Australian cities move on a weekly cycle, so the day you fill matters as much as the brand. A few simple habits do most of the work.
| Tactic | Why it helps |
|---|---|
| Buy only the octane your car specifies | Paying for 98 on a 91 engine is money gone for no gain |
| Fill mid-week | Prices often bottom out on a Tuesday or Wednesday before climbing toward the weekend |
| Use a fuel price app | Apps like Fuel Daddy show live prices nearby across QLD, NSW, VIC, TAS and WA, so you skip the dear stations |
| Lock in a low price | Some retailer apps, like the 7-Eleven app, let you hold a low price for a few days before you fill |
| Do not run to empty | On fumes you take the closest station, not the cheapest, so plan ahead |
| Consider warehouse fuel | Membership outlets like Costco often price several cents under the market average |
| Drive smoothly and keep tyres inflated | Hard acceleration and soft tyres both burn extra fuel |
None of these need a big lifestyle change. Checking an app before you pull in and filling on the cheaper day of the week does most of the work, and running the right octane does the rest.
Does the Fuel You Use Affect Resale Value?
Not directly, but running the correct fuel and looking after the car does. No buyer inspects a receipt to see which pump you used, and fuel choice alone will not move an offer. What moves an offer is condition and service history. A car fed the fuel its engine was built for, on top of regular servicing, tends to show cleaner internals, smoother running and less carbon buildup than one that was neglected, and that is what a buyer or dealer is really paying for. Our guide on 10 tips to preserve the value of your car covers the rest of the habits that hold a price.
If you are weighing up a sale, the fuel in the tank matters far less than knowing the car's real market value and having your paperwork straight. Our car valuation tools give you a realistic figure to work from, our guide on how to sell a car in Queensland walks through the process, and here is the paperwork you need to sell a car privately. For Brisbane car buyers a private sale can drag on for weeks, which is where selling to a licensed dealer saves the hassle.
We buy across South East Queensland, whatever fuel the car runs on. That includes used car buyers in Brisbane, the Gold Coast, Sunshine Coast, Toowoomba and North Lakes.
We buy cars across SE QLD whatever fuel they run on, petrol, diesel, hybrid or EV. Free pickup, no haggling, and same-day bank transfer once we agree a price.
Get a price for your carFrequently Asked Questions
Is unleaded 91 the same as E10?
Not quite. Both are around 91 octane at the pump, but E10 has up to 10% ethanol mixed in and standard unleaded 91 has none. They perform much the same in a car that accepts both, but the ethanol in E10 can affect older engines and fuel systems that were not built for ethanol blends. That is the one real difference worth knowing.
Can I use unleaded 91 instead of E10?
Yes, in almost every case. If your car runs on E10, it will also run on standard unleaded 91, and many drivers prefer 91 for the slightly better economy. Check the manual first, because a few newer cars are optimised for E10 and may show a small drop in efficiency without it, but 91 will not harm them.
Can I mix 91 and 98 in the same tank?
Yes, mixing octanes in one tank is safe. The fuels are compatible, so topping up with 98 when the tank still has 91 in it just gives you a blend somewhere in between. It will not harm the engine. The only thing to watch is that if your car requires 98, a tank that is mostly 91 sits below the minimum, so top back up to full 98 at the next fill.
Will using the wrong petrol damage my engine?
Using a higher octane than needed does no harm, it only wastes money. Using a lower octane than the car requires is the risk. On an engine built for 98, running 91 can cause knock, and sustained knock can damage the engine over time. Modern cars pull timing to protect themselves, which shows up as lost performance and worse economy rather than instant damage, but it is not something to make a habit of.
Is E10 safe for older cars?
Most petrol cars built from around 2005 onward are approved for E10, but many older vehicles are not, because ethanol can affect certain seals, hoses and fuel system parts. Never assume. Check the fuel flap sticker or the manual, and if you cannot confirm it, stick to standard 91.
Do turbo cars need premium fuel?
Many do, but not all, so check the manual rather than assume. Turbocharged engines often run higher compression and are tuned for 95 or 98, and on those the premium is not optional. Some smaller turbo engines are rated to run on 91. The fuel flap will tell you the minimum, and with a turbo it is worth respecting.
Does petrol go off if the car sits for months?
Petrol does degrade over time, generally staying usable for a few months in a sealed tank before it starts to lose quality. E10 can degrade a little faster because ethanol attracts moisture. If a car has sat unused for a long stretch, the fuel is one of several things worth checking before you rely on it.
Sell Any Car Fast is a licensed QLD motor dealer (DLN 4871214). This guide is general information about fuel choice, not mechanical advice. Always check your vehicle's manual or fuel flap for the fuel your specific car requires.
