What the octane number measures
In the cylinder, the air and petrol mixture should only burn when the spark plug fires. If pressure ignites it first, the engine knocks, which costs power and can damage the pistons over time.
The number on the pump is the Research Octane Number (RON). The higher it is, the more compression the petrol tolerates before it ignites on its own.
Which petrol to choose
Follow the manufacturer's recommendation, written in the owner's manual and usually inside the fuel filler flap. If your car asks for 95, a higher octane petrol does not normally bring measurable power or savings.
- Engine that asks for 95: standard petrol is enough.
- Turbo or sports engine that asks for 98: use 98, otherwise the electronics retard the timing and cut power.
- Never use a lower octane than recommended.
Octane and price
Premium petrol costs more because of its higher octane and, usually, cleaning additives. Today's price gap is on the premium petrol page.