Posting from the UK here.. If you have a 12 Gal (US) fuel tank and you wish to turn that EN228 Regular 95 fuel you get, into 100RON you could add up to 23.76% of the tank capacity with a 50/50 mix of Toluene and Xylene. Toluene for the RON, Xylene for the MON, you'll end up with 96 AKI racing grade. From where I've looked (eBay) cost-wise it would be a 60% price increase in filling up the tank. However, the gap from 90AKI to 100AKI decreases by 60%, going from 90AKI to 96AKI.