Long-term results of model biogas purification studies in a large-scale hollow-fiber-contained liquid membrane permeator containing 7008 hydrophobic microporous polypropylene hollow fibers are presented. The liquid membranes used were either pure water or an aqueous 20 wt.% diethanolamine (DEA) solution. Gas mixtures containing CO 2 and N 2 or CO 2 and CH 4 were utilized as feed. Steady and stable separation performance was observed for both passive and facilitated transport membranes.