For one of my cars the manufacture recommends premium fuel, so I use 99 octane at the petrol station. It contains 5% ethanol. At the same UK petrol station there is regular petrol with 95 octane, which contains 10% ethanol.
What’s the ethanol level in the US?
I believe the octane rating in the US is measured differently to the UK. You may be aware that in the UK the “Research Octane Number” is used. In the US they use an average of the Research Octane Number (RON) and Motor Octane Number (MON). Meaning a US rating of 91 octane is pretty much same as 97 octane in the UK.