The performances of a novel rapid pressure swing adsorption system for continuous production of similar to 90% O-2 from a compressed air feed were experimentally studied using two different samples of pelletized LiLSX zeolite. Bed size factor (BSF) and O-2 recovery (R) were compared as functions of total process cycle times. The optimum performance by the samples differed substantially-one exhibiting similar to 30% smaller BSF and similar to 6% higher R than the other, even though the adsorption isotherms and column dynamics for the pure gases were nearly identical. Column pressure drop during the desorption step was the cause.