The adsorption of ethane from helium was measured in beds packed with 2.5 mu m zeolite crystals and containing either a single hollow fiber or multiple fibers. The single-fiber experiments indicate that the mass-transfer rate in beds containing zeolite 13X is limited by diffusion across the fiber wall and through macropores. For adsorption in single-fiber beds packed with zeolite 4A, mass transfer is limited by micropore diffusion within the particles. Breakthrough curves from beds containing 13X are adequately described with the linear driving force model while curves from beds containing 4A are consistent with the Rosen model. Breakthrough curves from beds packed with zeolite 13X and containing multiple fibers can be predicted from the experiments with single-fiber beds when the fibers are evenly spaced. When fibers are unevenly spaced, the breakthrough curves are more disperse. Unevenly spaced fibers are the normal case. Even when fibers are evenly spaced, the productivity of hollow-fiber beds is expected to be no greater than that in conventional beds.