On the subject of "Octane Rating" there are two different scales, a but like Centigrade and Farenheit for temperature.
In the USA they use something called the "Anti Knock Index or AKI", we use the RON or Research Octane Number. The AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. So when we talk about 99 RON, which is premium gasoline in Europe the same in the USA is 93 Octane in the USA.
AVGAS is usually 100 octane and lead free versions are now available. Lead Free AVGAS works wonderfully in cars, it has a long shelf life and is both ethanol free and has a very low water content. But get caught using it and HMRC has a sense of humur failure: it has a lower fuel duty rate than motor fuel yet it costs about 30p/L more than car fuel.
It is still possible to get 115/145 Octane AVGAS, it contains 1.29g/L tetra ethyl lead..but big old radial engines must have it!
