A dynamic model of small valveless pressure swing adsorption (PSA) and vacuum and pressure swing adsorption (VPSA) units for the production of oxygen was developed for the purpose of simulation and optimization. This valveless operation, very often used in commercial units, results in a more complex cycle than the classic Skarstrom cycle, differing in the optimization conclusions and presenting specificities that cannot be ignored in the modeling and simulation. Three different commercially available adsorbents were evaluated for use in these units: Oxysiv 5 and Oxysiv 7 from UOP and SYLOBEAD MS S 624 from Grace Davison. The units' performances (product recovery and power consumption) using each adsorbent were compared for cycles with the same pressure ratio. The simulation results were found to be in agreement with experimental results obtained on a commercial unit.