Measurements of the sorption isotherms (at 298 K) for Ar, O-2, and N-2 in several polyaniline emeraldine base (PANi-EB) forms were made (as-cast film, powder, and fully undoped film) over the pressure range 100-1300 kPa. Model fits of the sorption isotherms were made using a modified Flory-Huggins equation (MFHE) and a dual mode sorption equation. In general, the variation of parameters for the MFHE was consistent with morphological interpretations from prior X-ray scattering studies. The ordering of gas sorption with respect to a particular PANi-EB form correlates with the relative sizes and condensabilities of the gas molecules. We see evidence that the morphological variations between different PANi-EB forms, as indicated by their He densities and X-ray scattering data, affects the ratio of O-2/N-2 solubilities primarily through restricted access to available free volume. From our current measurements of solubilities and prior results for the O-2 and N-2 permeabilities, we conclude that the O-2/N-2 ideal separation factor is due to diffusivity selectivity in an as-cast PANi-EB him and solubility selectivity in a fully undoped one.