What is RON in a car?

RON stands for Research Octane Number, and is a measure of the quality of fuel used in the UK and Europe – North America, conversely, uses octane. In the UK you'll find 95 RON petrol sold as regular unleaded, otherwise known as E10, and 97, 98 or 99 RON sold as super-unleaded, or E5 petrol. Most modern petrol cars in the UK are perfectly happy running on 95 RON fuel, although some high-performance cars run better on the upgraded fuel.