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Recommended means the manufacturer has designed the engine to run on regular 91 RON, but has calibrated it to extract a small performance or efficiency benefit from higher-octane fuel. In practice, modern engine control units (ECUs) are smart enough to detect lower-octane fuel and adjust ignition timing accordingly. The performance gap between 91 and 95 in a car that only "recommends" premium is, in most cases, negligible.

For the overwhelming majority of Australians driving a family SUV, hatchback, or sedan, the fuel cap says "recommended," which means 91 RON is perfectly fine.

When premium fuel is genuinely worth it

There are two clear situations where the higher-octane spend is justified.

The first is when it's required. If your car specifies a minimum of 95 or 98 RON, you should use it. This applies to performance cars with high-compression engines, turbocharged sports models, and many European vehicles. Think used Volkswagen Golf GTI, used BMW M2, or any used Porsche. These engines operate at compression ratios where regular fuel can cause knock, and that knock causes damage.

The second situation is when fuel economy matters enough to do the sums. Some engines with a "recommended" rating will return measurable economy gains on 98 RON, particularly under load or at highway speeds. But the maths rarely work in your favour. If 98 RON costs 15–30 cents per litre more and your car returns a 2–3% economy gain, you'd need to drive very long distances before the fuel saving offsets the price premium.

If you're noticing a higher consumption rate regardless of fuel type, that's a different issue worth investigating. Our guide on why your car might be using more petrol than expected covers the most common causes.

The ECU does the heavy lifting

Modern cars are not the carburettor-fed engines of the 1980s. Most vehicles built in the last decade come with adaptive engine management systems that monitor combustion in real time and pull timing back when they detect a lower-octane fuel. The result is a slight drop in power output, but rarely anything a driver would notice on the road.

Some manufacturers, including Toyota and Mazda, design their naturally aspirated engines with 91 RON as the base, meaning the engine is fully optimised for regular fuel already. Putting 98 RON in a used Toyota Corolla, for example, is not going to improve your morning commute.

The industry's vague language around "recommended" versus "required" leaves a lot of drivers uncertain and inclined to spend more just to be safe. It's the kind of murky specification that benefits nobody. Carma takes a similar approach to transparency in a different part of the car-buying process: one fixed price, no negotiation, no wondering if you paid more than the person before you.

Which cars actually need premium fuel

As a rough guide, these are the vehicle types where 95 or 98 RON is typically required or delivers a meaningful benefit:

• Turbocharged performance engines: used Ford Mustang GT500, used Volkswagen Golf GTI, used Subaru WRX, used BMW M-series
• High-compression naturally aspirated engines: many used Mazda SkyActiv-X engines, some used Lexus and Audi models
• European luxury vehicles: check the manual, as many Mercedes-Benz and Audi models specify 95 RON as a minimum
• Older high-performance engines: pre-2000 performance cars often lack the ECU sophistication to adjust for lower octane

If your car doesn't appear on a list like this, check the manual. The manufacturer's specification is the only source that matters.

The verdict for everyday drivers

Does premium fuel make a difference? For performance cars with engines that require high-octane fuel, yes. For the vast majority of Australian drivers in everyday cars, no. You're spending real money for a benefit so small it's practically unmeasurable.

Check the fuel cap. If it says "required," use the grade specified. If it says "recommended," save your money and put regular in. Your ECU is handling the rest.

When you're ready to find a used car that suits your budget and driving style, Carma lists every car with full specs, including the fuel type required, so you know exactly what you're getting before you buy.