What Does RON Mean?
RON stands for Research Octane Number — a measure of a fuel's resistance to “knocking” (premature combustion in the cylinder). Higher RON means the fuel can withstand greater compression before igniting, which is essential in high-performance, turbocharged, and modern direct-injection engines designed to take advantage of it.
A standard naturally aspirated engine designed around 91 RON does not benefit from higher octane fuel. The engine management system is not programmed to advance timing beyond what 91 RON safely allows. You get no more power, no better economy, and no engine protection benefit from using 95 or 98 in a 91-RON vehicle.
However, in an engine specifically tuned for higher octane — such as a high-compression turbocharged unit — using the correct grade allows the engine management system to run optimal ignition timing, maximising both power output and fuel efficiency. In these cases, using lower octane than specified actually hurts performance and may worsen economy.
Fuel Grade Comparison
E10 (Ethanol 10%)
- Octane:
- 94 RON equivalent
- Price:
- Usually cheapest option (-2 to -5¢/L vs 91)
- Good for:
- Most cars manufactured after 2000 that specify E10 compatibility
- Avoid if:
- Older vehicles, boats, small engines, motorcycles (check manual)
Contains 10% ethanol. Slightly lower energy density than 91 unleaded, which can reduce fuel economy by 2–3% in some vehicles. Net cost saving depends on your specific fuel economy impact.
91 RON Unleaded
- Octane:
- 91 RON
- Price:
- Baseline regular price
- Good for:
- Any vehicle that requires 91 RON minimum or is E10 incompatible
- Avoid if:
- Vehicles that require 95 or 98 RON (check your fuel cap or manual)
Standard unleaded. The most widely available grade and the benchmark for the Melbourne price cycle. If your car specifies 91 minimum, this is the most cost-effective choice.
95 RON Premium
- Octane:
- 95 RON
- Price:
- Typically 10–20¢/L above 91 RON
- Good for:
- Vehicles that recommend or require 95 RON minimum
- Avoid if:
- Standard vehicles that only require 91 — you pay more with no benefit
Higher octane rating reduces the risk of engine knock in high-compression engines. If your car manual says "recommended: 95 RON" you will get the intended performance and may see marginally better economy vs 91 in performance-tuned engines.
98 RON Premium
- Octane:
- 98 RON
- Price:
- Typically 20–35¢/L above 91 RON
- Good for:
- Vehicles that require 98 RON, high-performance sports cars, modern turbocharged engines tuned for premium fuel
- Avoid if:
- Any vehicle that specifies 91 or 95 minimum — a significant waste of money
Highest octane available at most Melbourne pumps. Genuine performance and economy benefits are only realised in vehicles specifically engineered for it. In a standard family car requiring 91 RON, 98 premium provides zero measurable benefit over 91.
The Real Cost of Using the Wrong Grade
In Melbourne, the price gap between 91 unleaded and 98 premium is typically 20–35 cents per litre. On a 60-litre tank, that is $12–$21 extra per fill-up. Over a year of weekly fills, upgrading unnecessarily from 91 to 98 costs $625–$1,092 with no benefit.
Conversely, drivers who need 95 or 98 and consistently use 91 may experience reduced performance and, in some turbocharged engines, very marginally worse economy — meaning the per-kilometre cost is sometimes not much lower than using the correct grade despite the cheaper pump price.
The correct approach is simply to use the grade your manufacturer specifies. This optimises both cost and performance simultaneously.
E10: The Cheapest Option — But Is It Right for You?
E10 (91 RON equivalent with 10% ethanol content) is typically 2–5¢/L cheaper than standard 91 unleaded and is compatible with most modern vehicles. The main practical difference is a slight reduction in energy density: ethanol contains less energy per litre than petrol, so fuel economy in E10 vehicles may drop by 1–3% depending on the vehicle.
For most drivers, the cheaper pump price more than offsets the marginal economy reduction. But for vehicles with older fuel systems, E10 is not recommended due to potential compatibility issues with certain seals and components. Check the E10 compatibility list on your state fuel authority website if your vehicle is pre-2000 or you are unsure.