Must admit, I haven't looked into the science behind mixing of chemical components
(e.g. partial pressures, relative densities etc.), but wonder about the compounds involved;
in liquids oil & water will separate into distinct layers due to different densities/polarities,
but water & ethanol will mix despite having different densities.
As for gasoline, it's a mix of hundreds of compounds of different densities/polarities
(and I suspect, by the science of it's distillation, would condense out at different temperatures)
in air (a mix of different gases of different densities/polarities; admittedly not separating);
add moisture (water being polar, and separating out at it's dew-point temperature)
and you have a party mix beyond my (admittedly-limited) mental abilities.
Suspect the partial pressures of the myriad of compounds comprising gasoline would sit either side that of water's...