<p>The influence of the parameters of the porous substrates of composite membranes on the efficiency of desorption of CO₂ and O₂ from the 30% aqueous solution of methyldiethanolamine in gas–liquid membrane contactors was investigated. The composite membranes formed on the polysulfone and polyphenylene sulfone substrates with a nonporous layer of a mixture of poly[1-(trimethylsilyl)-1-propyne] and poly(vinyl trimethylsilane) were compared. It was established that, in the case where the thickness of the nonporous layer of such membranes varies within a small range, their permeability is determined mainly by the properties of the membrane substrate. Experimental data were supported by the calculations of the mass transfer through the indicated membranes. The results obtained can be useful for the optimization of the membrane modules in systems for regeneration of amine adsorbents.</p>