ULP 91 vs PULP 95 vs 98 RON: Which Fuel Should You Use?

Stand at a fuel bowser in Perth and you will typically see at least three grades of petrol: ULP 91, PULP 95, and 98 RON. Prices can vary by 15 to 25 cents per litre between the cheapest and most expensive grade. So what is the actual difference, and when does it make financial sense to pay extra?

What does RON mean?

RON stands for Research Octane Number. It measures a fuel's resistance to "knocking" or "pinging" inside an engine. Knock occurs when the air-fuel mixture in a cylinder ignites prematurely before the spark plug fires, causing an audible rattling sound and potentially damaging the engine over time.

A higher RON number means the fuel can withstand more compression before spontaneously igniting. This is important because modern high-performance and turbocharged engines operate at higher compression ratios to generate more power from the same engine displacement.

ULP 91: standard unleaded

ULP (Unleaded Petrol) with a RON of 91 is the minimum petrol grade sold in Australia and the baseline fuel for most everyday vehicles. The majority of Australian car sales over the past two decades have been standard four-cylinder passenger cars (Toyota Corolla, Mazda 3, Hyundai i30, etc.) that are designed to run perfectly well on 91 RON.

ULP 91 is typically the cheapest petrol at the bowser — often 8 to 18 cents per litre less than 95 RON and 15 to 25 cents less than 98 RON. If your vehicle's owner manual specifies "minimum 91 RON" or just "unleaded petrol," you do not need anything higher.

PULP 95: the middle ground

PULP (Premium Unleaded Petrol) 95 is the most common recommendation for turbocharged and higher-performance engines found in modern mid-range vehicles. Many European cars (VW, BMW, Audi, Mercedes-Benz) specify a minimum of 95 RON. Similarly, Mazda's SkyActiv engines, Ford's EcoBoost range, and many recent SUV turbos call for 95 as the minimum.

Using 91 RON in a 95-RON car is not catastrophic — modern engine management systems will retard timing to prevent knock — but you will lose some power and fuel efficiency, potentially offsetting the cost savings of the cheaper fuel. Over time, the knock retardation also generates more heat in the combustion chamber, which is not ideal for turbocharged engines.

98 RON: premium performance

98 RON is the highest grade commonly available at Australian servos. It is necessary for high-performance sports cars, luxury vehicles, and any car whose manufacturer specifies "98 RON" or "super premium" fuel. Examples include the Porsche 911, BMW M-series, Ford Mustang GT500, Subaru WRX STI, and most supercars.

For these vehicles, 98 RON allows the engine management system to run optimal, more aggressive ignition timing, delivering maximum power output as the manufacturer intended. Running on lower-octane fuel in a 98-RON-required car will result in noticeable power loss and, in severe cases, engine damage from prolonged knock.

Which fuel does your car need?

What your manual says	Minimum you should use	Upgrade worth it?
"Unleaded" / "91 ULP"	ULP 91	Generally no benefit
"Premium unleaded" / "95 RON minimum"	PULP 95	Possible small gain from 98 RON in hot weather
"98 RON" / "Super premium required"	98 RON	Yes — use 98 as specified
"91 RON or higher recommended"	ULP 91 minimum	Possibly, for turbocharged variants of the same model

The single best source for your fuel recommendation is your car's owner manual, not the fuel cap sticker (which sometimes shows a simplified label) and not the advice at the bowser. When in doubt, a quick search for your exact vehicle make, model, engine, and year will give you the definitive answer.

Is premium fuel worth the extra cost?

For cars that only recommend (not require) premium fuel, the economic case for upgrading is usually weak. Studies and real-world testing in Australia consistently show that for vehicles where 91 RON is acceptable, running 95 or 98 RON delivers perhaps a 1-3% improvement in fuel economy, which is far less than the 8-20% premium in price.

In Perth, when 91 RON is 175 cents/litre and 95 RON is 190 cents/litre, the 91-RON car would need to achieve at least 8.6% better fuel economy on 95 RON just to break even. That simply does not happen in practice for a standard engine.

For cars that genuinely require 95 or 98 RON, the cost is unavoidable — but you can still save money by choosing the right time of week to fill up and by comparing prices across nearby stations using EconomicWatch.

Engine knock and long-term engine health

All modern cars sold in Australia have knock sensors — electronic sensors that detect the vibration signature of engine knock and immediately retard ignition timing to eliminate it. This means that filling a 95-RON car with 91 RON will not cause immediate or dramatic damage: the ECU will compensate. But persistent fuelling below the recommended grade means the knock sensor is constantly compensating, the engine never runs at its optimal tuning, and combustion temperatures are higher than intended. For turbocharged or high-compression engines, this is a long-term concern.

The key principle: never use a lower RON than your manufacturer requires. Using a higher RON than required is not harmful but is generally a waste of money.

A note on E10 ethanol blend

E10 is a blend of 90% petrol and 10% ethanol sold at some WA stations. Technically classified as 94 RON despite the higher octane number from the ethanol content, E10 contains about 3% less energy per litre than ULP 91. This means slightly higher fuel consumption (roughly 2-3%), partially offsetting any price benefit. E10 is suitable for most modern cars but check your owner manual, particularly for vehicles manufactured before 2005 and for small engines in lawn mowers or marine equipment.