Dynamic simulation with the valve equation approach of a four-bed pressure swing adsorption (PSA) process for oxygen enrichment over zeolite 5A was performed. Product pressurization, feed pressurization, production, blowdown, purge, and pressure equalization are included in this process. The numerical results were compared to the experimental results of Chiang et al. (1994) and gave reasonable agreements. The effects of production rate and purge rate on the purity and recovery were also explored by simulation. When breakthrough did not occur for the depressurizing bed during the pressure equalization step, operation at the minimum purge rate gave a relatively high recovery for producing a product of purity more than 95% oxygen. When breakthrough occurred, the theoretical results show that, for a fixed production rate, there is a purge rate giving the maximum recovery and a different purge rate giving the highest purity.