An experimental study of the diffusion and permeability coefficients of helium, oxygen, and nitrogen in membranes prepared by solvent casting of commercial poly(vinyl chloride) (PVC) is reported. Transport parameters are very sensitive to the densification of PVC so that at 25 degreesC a sharp drop in the values of the permeability and solubility coefficients during the first week takes place. The variation of the transport parameters with aging time is nearly negligible after one month. Molecular dynamics methods were used to simulate a host matrix of poly(vinyl chloride) with density similar to that of the aged polymer. The application of the transition states approach to the simulation of the diffusion of gases in poly(vinyl chloride) gives values of the diffusion coefficient somewhat lower than the experimental ones for oxygen and nitrogen and higher for helium. Gas solution in poly(vinyl chloride) was simulated by means of a Monte Carlo cycle that inserts, with probability p(in), or removes, with probability p(re), particles of diffusant at randomly selected positions within the polymeric matrix. The values of the permeability coefficients calculated from the simulated diffusion and solubility coefficients are in very good agreement with the experimental results.