Sorption of different gases (N-2, O-2, CH4, and CO2) were performed on as-synthesized polyemeraldine base, on HCl 4M doped, on NH4OH 1M undoped, and on HCl 10(-2) M redoped powders. In the pressure range examined (100-700 torr), linear sorption isotherms were observed for N-2 and correspond to an ordinary dissolution in Henry’s law state. Concerning O-2, CH4, and CO2, nonlinear isotherms were evidenced and could be described by the dual-mode sorption mechanism proposed for glassy polymers, which consists of the combination of a Henry’s type dissolution with a Langmuir sorption in unrelaxed gaps between macromolecular chains. Specific interactions between polyaniline (PANi) and O-2, CH4, and CO2 were studied. Gas permeation experiments were performed by using different upstream pressures, P-1, and have confirmed the dissolution of Henry’s type for N-2 and the dual-mode mechanism for O-2 and CO2. From the fits of the sorption isotherms, gas solubilities of N-2, O-2, CH4, and CO2 were calculated for three different gas pressures and analyzed in terms of gas separation for permeation experiments.