98 octane i use , i can see the differance between useing both oils , i use to use the motul 800 and still useing the same fuel when useing motorex and it cleaner, and a lot easier to clean the parts as well, i only tried motorex because vhm people said motul 800 was dirty and i notice it in a lot of 2t powervalves that it harder to clean off. vhm guys were right on the money.