Petrol or gasoline is assessed, categorised and sold by an octane rating. Generally, in most areas of the world, the Research Octane Number (RON) is used, but in North America, the Anti-Knock Index (AKI) is used. Conventional 'standard' "Super Unleaded" petrol in Europe, South Asia and Australia has an octane rating of 95 RON, and in North America "Premium Unleaded" is AKI/RdON/PON 91-93 (RON 96–98). However, higher octane "Super Plus Unleaded" - often formulated with higher quality additives, is usually set at around 98 RON in mainland Europe; but this can vary by market. Most oil/petroleum companies now 'market' their own Super Plus Unleaded petrols under a unique name - and the current name for Shell Super Unleaded fuel is "V-Power". Like most Super Plus Unleaded petrols, V-Power also contains higher concentrations of detergents and other additives to help clean the engine and smooth its operation.[2] In the United Kingdom and Denmark (where Super Plus Unleaded must be a minimum of 97 RON), V-Power has a rating of 99 RON (whereas V-Power's predecessor Shell Optimax was rated at 98 RON).[3] There are two other 99 RON fuel available in the UK, namely Tesco MOMENTUM99 and more recently both Costco Premium Unleaded (99 RON) and Esso Synergy Supreme+ 99.[4] In The Netherlands, V-Power used to have a 95 RON rating, although officials from Shell stated it effectively had a 97 RON rating. Due to the limited categories of 92 RON, 95 RON, 98 RON and 100 RON.,[5] it was officially rated at 95. These days, the RON rating of the V-power petrol in the Netherlands is rated at 98.[1] In Germany, all Shell stations offer V-Power Racing 100, rated at 100 RON.[citation needed]