E10 vs ULP91 vs ULP95 vs ULP98 — Which Fuel for Your Car in Australia?

Australian service stations sell up to four grades of petrol — E10, ULP91, ULP95, and ULP98. The price difference between the cheapest and most expensive can be 30 to 40 cents per litre, which adds up to hundreds of dollars a year. But cheaper is not always better. Choosing the wrong grade can hurt your engine, void your warranty, or cost you more per kilometre than the premium option. This guide breaks down exactly what each fuel is, which one your car needs, and which one actually saves you the most money.

What the Grades Mean

E10 — Ethanol Blend, 94 RON

E10 is a blend of 90% standard unleaded petrol and 10% ethanol. It carries a minimum Research Octane Number (RON) of 94, though the effective octane behaviour is broadly comparable to 91 RON unleaded for most engines. E10 is the cheapest petrol at the pump, typically 3 to 5 cents per litre less than ULP91.

The ethanol content means E10 has approximately 3% less energy per litre than pure petroleum-based ULP91. In practical terms, your car will use slightly more fuel to travel the same distance on E10. Whether the lower price offsets the lower economy depends on the price gap — we do the maths below.

ULP91 — Standard Unleaded, 91 RON

ULP91 (Unleaded Petrol 91) is the baseline petrol grade in Australia. It has a minimum octane rating of 91 RON and contains up to 5% ethanol (though many brands sell it with little or no ethanol). This is the fuel most Australian cars are designed to run on, and it is the reference point for pricing — E10 is cheaper, while ULP95 and ULP98 are more expensive.

Check ULP91 prices across Australia on our live tracker, updated daily from government data.

ULP95 — Premium, 95 RON

ULP95 (Premium Unleaded 95) has a minimum octane rating of 95 RON. It typically costs 10 to 15 cents per litre more than ULP91. Many European and Japanese imports manufactured after 2000 recommend or require 95 RON fuel. Using 91 RON in these cars can cause engine knock (a rattling or pinging sound under load), which the engine's knock sensor will detect and compensate for by retarding ignition timing — resulting in reduced power and potentially worse fuel economy.

You can browse ULP95 prices to find the cheapest premium unleaded near you.

ULP98 — Ultra Premium, 98 RON

ULP98 is the highest octane petrol available at Australian service stations. It costs 20 to 30 cents per litre more than ULP91 and is marketed as a high-performance fuel. Brands like Shell V-Power, BP Ultimate, and Ampol Amplify are all 98 RON products, and they typically include additional detergent and cleaning additives.

ULP98 is required by some high-performance and turbocharged vehicles. For cars that only require 91 or 95 RON, using 98 provides no meaningful performance benefit — the engine cannot take advantage of the higher octane rating, so you are paying more for nothing. See the latest ULP98 prices to check the premium you would be paying.

Ethanol Content

Ethanol content is one of the most misunderstood aspects of Australian fuel grades:

• E10: Contains exactly 10% ethanol by volume. This is mandated and clearly labelled.
• ULP91: May contain up to 5% ethanol. The exact amount varies by brand and batch. Some retailers sell ethanol-free ULP91, but it is not guaranteed unless specifically labelled.
• ULP95 and ULP98: Typically contain little to no ethanol, though regulations allow up to 5%. Premium fuels generally achieve their octane rating through refining processes rather than ethanol blending.

Ethanol is hygroscopic (it absorbs water from the atmosphere), which can cause issues in vehicles that sit unused for long periods. If you have a car, boat, or mower that is stored for weeks at a time, ethanol-free fuel is a better choice for the fuel system.

Engine Compatibility

The critical rule is simple: never use a fuel with a lower octane rating than your car's minimum requirement. Your owner's manual or the fuel filler cap will state the minimum RON. Here is the general picture:

• Most Australian-built and common Japanese cars (pre-2010): Designed for 91 RON. Can safely use E10, ULP91, ULP95, or ULP98.
• Modern European cars (VW, BMW, Mercedes, Audi, Volvo): Often require 95 RON minimum. Check the manual — using 91 RON may cause knock and will retard timing.
• High-performance and turbocharged vehicles: Many require 95 or 98 RON. Turbo engines are particularly sensitive to octane because they operate at higher compression and temperatures.
• E10 compatibility: Almost all cars manufactured after 2006 are E10 compatible. Some older vehicles (particularly those with certain rubber seals and fuel lines) may experience issues with ethanol. The Federal Chamber of Automotive Industries (FCAI) maintains a compatibility list if you are unsure.

Using a higher octane than required is not harmful — it simply costs more without providing a benefit. Using a lower octane than required can cause engine damage over time and will almost certainly void your warranty.

Fuel Economy Differences

Because ethanol contains less energy per litre than petroleum, E10 delivers approximately 3% fewer kilometres per litre than ULP91. The other grades (ULP95 and ULP98) have essentially the same energy content as ULP91 — the higher octane does not mean more energy, it means greater resistance to premature combustion (knock).

In a car that requires 95 RON, using 95 instead of 91 may actually improve economy slightly because the engine can run optimal timing without knock-sensor intervention. But in a car designed for 91 RON, stepping up to 95 or 98 will not improve economy at all.

Price Comparison and Cost per Kilometre

Here is a typical price ladder at an Australian metro station and the real cost impact:

*Effective cost adjusts for energy content difference. E10's effective cost = pump price / 0.97 to account for 3% less energy.

In this example, E10 looks 4 cents cheaper at the pump, but after adjusting for the 3% energy penalty its effective cost is 181.3 c/L — actually 1.4 cents more expensive per unit of energy than ULP91. Whether E10 saves you money depends entirely on the price gap. If E10 is more than about 5 cents cheaper than ULP91, the pump price saving outweighs the efficiency loss. If the gap is smaller, ULP91 is the better deal.

Compare today's E10 prices against ULP91 prices in your area to see whether the gap is wide enough to make E10 worthwhile.

When to Use Each Grade

E10 — Best For

• Budget-conscious drivers with compatible vehicles (most post-2006 cars)
• City driving where the 3% economy difference is negligible
• Situations where E10 is more than 5 cents cheaper than ULP91
• Drivers who fill up frequently (ethanol absorbs moisture over time, so frequent use avoids issues)

ULP91 — Best For

• Most standard Australian cars that specify 91 RON minimum
• Vehicles that are stored for extended periods (less ethanol concerns)
• When the E10 price gap is less than 5 cents per litre
• Small engines, mowers, boats, and generators (many manufacturers advise against ethanol)

ULP95 — Best For

• Vehicles that specify 95 RON minimum (many European and newer Japanese imports)
• Turbocharged four-cylinder engines that require 95 RON
• Drivers who want a balance between cost and engine protection for 95-RON cars

ULP98 — Best For

• High-performance vehicles that require 98 RON (check the fuel filler cap)
• Towing heavy loads or driving in sustained high-temperature conditions
• Track days or spirited driving where maximum engine performance matters
• Drivers who want the additional detergent additives included in most 98 RON products

Common Myths Debunked

"Premium fuel cleans your engine"

Partly true, but overstated. ULP98 products like Shell V-Power and BP Ultimate do contain extra detergent additives that can help keep fuel injectors and intake valves clean. However, all fuel sold in Australia must meet minimum detergent standards. The cleaning benefit of premium fuel is real but modest — it will not fix an already dirty engine, and it does not justify the 20 to 30 cent premium if your car only requires 91 RON. A bottle of fuel system cleaner from a parts store costs $10 to $15 and does the same job more effectively than running a single tank of premium.

"E10 damages fuel systems"

This was a legitimate concern with older vehicles built before ethanol blends were common. Cars manufactured after 2006 are designed to handle E10 without issues. The rubber seals, fuel lines, and fuel pump materials in modern vehicles are ethanol-compatible. If your car is pre-2006, check the FCAI compatibility list. If it is newer, E10 is perfectly safe.

"Higher octane means more power"

Only if your engine can use it. Octane rating measures resistance to knock, not energy content. A car designed for 91 RON extracts no extra power from 98 RON fuel — the engine management system does not advance timing beyond its 91 RON calibration. You get more power from higher octane only in engines specifically tuned to take advantage of it (those that require 95 or 98 RON).

"You should run a tank of premium every few months"

This is a persistent myth with no engineering basis. If your car requires 91 RON, running a tank of 98 RON occasionally does nothing beneficial. The small amount of extra detergent in one tank has negligible cleaning effect. Use the fuel grade your car is designed for, every time.

How to Find the Best Price for Your Grade

Once you know which fuel your car requires, the next step is finding the cheapest station selling that grade. Prices for the same fuel type can vary by 15 to 25 cents per litre within a single suburb. Over a year of weekly fill-ups, choosing the cheapest station consistently can save $400 to $600.

Use compare prices near you to search by postcode or suburb. You can filter by fuel type to see only the grade you need. We also have dedicated pages for diesel prices if you drive a diesel vehicle.

For state-specific pricing, check WA prices and NSW prices. For a broader look at why prices differ by location, read our state-by-state guide.

Frequently Asked Questions

Can I switch between E10 and ULP91?

Yes, absolutely. If your car is E10 compatible (most post-2006 vehicles), you can switch freely between E10 and ULP91 from fill-up to fill-up. You can even mix them in the same tank with no issues. Many drivers use E10 when the price gap is wide and switch to ULP91 when the gap narrows. There is no need to empty the tank or add any additives when switching.

Is ULP98 worth the extra cost?

Only if your car requires it. If your manual specifies 98 RON minimum, you must use it. If your car requires 95 RON, ULP98 is safe but offers no measurable benefit over ULP95. If your car requires 91 RON, ULP98 is a waste of money — you will see no improvement in power, economy, or engine cleanliness that justifies the 20 to 30 cent per litre premium. Over a year, the difference between ULP91 and ULP98 on weekly fill-ups is roughly $600 to $900 — enough for a service and new tyres.

What if my car requires 95 RON?

Use ULP95 or ULP98 — never ULP91 or E10. Using fuel below your car's minimum octane requirement can cause engine knock, reduced performance, increased emissions, and potential long-term damage. It may also void your warranty. ULP95 is the more cost-effective choice for 95-RON cars; ULP98 is safe to use but typically offers no additional benefit.

Does E10 reduce my fuel economy?

Yes, by approximately 3%. Ethanol has about 33% less energy per litre than petrol, and since E10 is 10% ethanol, the net energy reduction is roughly 3%. In real-world driving, this means if you get 10 L/100km on ULP91, you might get 10.3 L/100km on E10. Whether the pump price saving outweighs this depends on the price gap — if E10 is more than 5 cents cheaper per litre, you come out ahead despite the lower economy.

Is it bad to mix fuel grades?

No. Mixing different octane grades simply gives you a blend with an intermediate octane rating. If you put half a tank of ULP91 and half a tank of ULP95, you effectively have a tank of 93 RON fuel. This is fine for any engine. The only rule is not to go below your car's minimum requirement — so if your car needs 95 RON, do not add ULP91 even as a top-up, as the blended octane will be below 95.