Research Octane Number (RON)

In the UK, the two standard pump grades are: E10 (RON 95 minimum) — standard unleaded, blended with up to 10% ethanol; and premium unleaded (sometimes labelled V-Power, Momentum 99, or Ultimate) at RON 97–99.

Whether premium fuel is worth paying extra for depends on your engine. Modern turbocharged engines (common in BMWs, Volvos, modern Fords, Volkswagens) are designed to benefit from 97–99 RON fuel — their engine management systems can advance the ignition timing, extracting more power and sometimes better fuel economy. Independent tests suggest a 2–5% MPG improvement in suitable engines, which at typical price premiums of 8–12p/L may or may not pay for itself.

For naturally aspirated, older, or smaller engines, the benefit of premium fuel is typically zero. The engine has no way to take advantage of the extra knock resistance.

RON is distinct from the AKI (Anti-Knock Index) used in the US, which is approximately 4–5 points lower. US '91 premium' is roughly equivalent to UK '95 standard'. UK drivers importing US car specifications should note that 'requires 87 octane' in the US means standard 91–92 RON UK petrol — not premium.

WorthThePump currently treats petrol as a single fuel type. Premium vs standard petrol price differences are not modelled in the detour calculation.