As far as I know there are no two gasses that don't mix (excluding demixing by gravitational effects). For me, as someone working with fluids and surface tensions a lot, this means that the surface tension between the gasses is small or even non-existent.
I saw in this post that mixing will be governed by the Gibbs free energy: $\Delta G = \Delta H - T\Delta S$ and that the only thing stopping fluids from mixing would be the enthalpy term which arises from repulsion.
Is it correct to think that the enthalpy will always be small in gasses, because of their low density and thus low interaction? And that this is the cause that gasses will always mix?
(just a footnote: I am talking about 'everyday' gasses here, not gasses compressed at thousands of bars with densities close to liquids)