My understanding is that 100LL has a relatively low volatility to reduce the
chance of vapor lock. Whereas Mogas often has a higher volatility.

With this in mind, what happens to the volatility if I mix 50% 100LL with
50% Mogas? Is the volatility of the mix the straight average of the two
fuels, or is the net volatility higher than the straight average?

Why do I ask? I'm considering running a "mix" in the RV-6 to save a few
bucks. The FBO at my home field charges about $2.00/gallon more for 100ll
than the nearby station charges for 93 octane, so a couple of 5 gallon tanks
worth of fuel will save me $20 bucks.