As others have indicated, it is possible to get synergistic effects, but it has not been mentioned that the opposite is also possible.
Commercially available fuels for highway use do vary in composition from grade to grade, from supplier to supplier, from season to season and from region to region.
To try to predict the outcome of blending, without knowledge of all the components in both fuels, would be a very risky thing to do. Just my opinion, but you will most probably get a weighted average octane, but it could also be better or worse than either component on it's own, or somewhere in between.
Regards
pat pprimmer@acay.com.au
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