In this study, preparation and simulation of polydimethylsiloxane (PDMS) membranes for gas separation is carried out. The membranes are synthesized by solution-casting method via silicon oil as precursor. Gas permeation experiments for single gases of CH4 and N2 were conducted at different feed pressures (2–10 bars). PDMS membrane as a rubbery polymer showed that are more permeable toward more condensable gases, i.e., CH4 compared to N2. It was indicated that increasing feed pressure enhances permeability of CH4 through the membrane slightly, but the permeability of nitrogen was almost constant over enhancement of feed pressure. Moreover, a mathematical model was developed to predict the permeation of gases across PDMS membrane. The model is based on solving conservation equations for gases in the membrane phase. Finite element analysis was utilized for numerical simulation of the governing equations. The simulation results were used to predict the concentration of gases inside the membrane. POLYM. ENG. SCI., 2014. © 2014 Society of Plastics Engineers