Need I tell you that it is complicated in the US? States, or groups of states, have different regulations. In California we use the formula RON + MON / 2. Then we have what we laughingly (or cryingly) call the "best congress money can buy". At the "urging" of agribusiness, they have mandated that we have to burn up a lot of good fuel to produce ethanol to lower our gas mileage.Gas/ petroleum in the UK and Europe is high octagon compared with the USA. I have run turbo petrol cars on standard 95 RON in the UK and the performance was no different than super unleaded or 98 RON.
I am guessing premium in the USA is standard fuel in Europe hence the fuel advice from Mercedes.
In CT, regular is typically listed as 87, midgrade/special is 89 and premium is generally 91 (maaaybe 93 if you can find it). Mobil's premium used to be 93, for example, but I think local regulations have altered the mix taking it down to 91. Doesn't Sunoco sell a "94" in some states? I believe those are considered "super" here.Wikipedia said:In the US, octane ratings in unleaded fuels can vary between 86 and 87 AKI (91-92 RON) for regular, through 89-90 AKI (94-95 RON) for mid-grade (European premium), up to 90-94 AKI (95-99 RON) for premium (European super).