How much more does RON 99 cost?
The latest UK averages available to Route & Fuel are 182.6p per litre for RON 99 and 162.2p for E10. The current difference is 20.40p a litre.
| Fuel added | Added cost compared with E10 |
|---|---|
| 30 litres | £6.12 |
| 45 litres | £9.18 |
| 55 litres | £11.22 |
The smaller rows show how the result changes with the amount bought. The website uses 55 litres as a consistent, realistic large-fill example; use the calculator or app for the litres you expect to buy.
To recover this added pump cost through fuel economy alone, the vehicle would need to travel about 12.6% farther per litre on RON 99 than E10. This is a break-even calculation, not an expected improvement for your car.
RON 99 and E10 average prices
The lines show recent UK averages, not a prediction or a guarantee that a particular station has RON 99 available.
What does a higher octane rating change?
RON measures a petrol fuel's resistance to engine knock. Some turbocharged or high compression engines can make use of higher octane fuel through their ignition timing or boost control, but the benefit depends on the engine and its software. Research from NREL and SAE shows that the response varies by engine design, load and calibration.
Is RON 99 worth it for a performance car?
If the manufacturer requires 98 or RON 99, use that grade. If premium petrol is recommended for full performance but 95 RON is also permitted, RON 99 may help the engine deliver the response it was designed for under heavier load.
Check the fuel flap, the owner's manual or the manufacturer's guidance. If 95 RON is the only grade specified, do not assume RON 99 will reduce your fuel bill.
What about remapped or tuned cars?
Use the octane grade specified by the tuner for the ECU map installed on the car. A remap can be calibrated for a particular fuel grade, so the factory recommendation may no longer describe the software you are running.
APR, for example, tells drivers not to use a lower octane than the tune requires. Other tuners offer separate maps or modes for different fuel grades. Follow the instructions for your own map and ask the tuner to confirm the fuel requirement.
Which UK fuels appear in the RON 99 search?
Route & Fuel currently groups these brands into its RON 99 search. Availability varies by site. Texaco remains in the wider RON 97+ search because its premium grade can vary by site.
| Retailer and fuel | Search group |
|---|---|
| Shell V-Power Unleaded | RON 99 |
| Tesco Momentum 99 | RON 99 |
| Esso Synergy Supreme+ 99 | RON 99 |
| Texaco Supreme | RON 97+ |
How can you compare RON 99 fairly?
- Confirm the grade required by the manufacturer or ECU tuner.
- Use the same fuel grade for several tanks rather than judging one short trip.
- Record the litres added and miles driven between comparable fills.
- Keep your usual route, load, driving style and tyre pressures reasonably consistent.
- Compare the actual cost per mile, then decide separately whether you value any change in performance or response.
Your car's MPG display can help show a trend, but litres bought and odometer miles give a better cost comparison.