[rotorwrench]

I missed the alcohol free BUT, leaded AVGAS is not made from the same base stocks so it's expensive to produce. It's also illegal to use for road fuel. It is a paraffin base with low vapor pressure where MOGAS is based on aeromatic hydrocarbons that have higher volatility.

Avgas's chemical nature or low volatility makes it necessary to use TEL (tetraethyl lead) in order to achieve it's octane rating. It is very stable so it lasts a lot longer in storage

Mogas is more volatile so it needs no TEL to be detonation resistant. Alcohol free Mogas can be used under STC (supplemental type certificate) in some aircraft engines after blending with Avgas to reduce vapor pressure if it's too high. A person can't pull over up there if the engine fuel system gets vapor locked so vapor pressure testing is required for each batch.

The STC warns of storing Mogas to be used in the aircraft. Even with no ethanol, the high volatility fuels break down enough after 6-months that a person should avoid use of it in an aircraft engine application. It might be fine for automobile use at lest for a while longer.