Can't say about two gasolines of close sp.gr. , but asphalt( sp.gr ~ 1.02 ) and
kerosene-(sp. gr. ~ 0.8 ) mix in any proportion and don't stratify--at least
not
in 20 or 25 years..

jls wrote:

Let's say you mix 1 part avgas with 3 parts mogas for use in your flying
O-300-powered demon. You have an STC for doing this, of course.

These two fuels have different specific gravities, so it is said. Do they
stratify? I don't believe they do. Anybody have a comment? I guess you
could pour samples into a glass tube and watch and see if they get it on or
avoid each other.