Permeabilities of N-2, Ar, O-2, CO2, and H-2 gases in PEMA (Polyethylmethaerylate) membranes have been measured above and below glass transition in the temperature range of 25-70 degrees C. The permeabilities of the gases were observed increasing with temperature. Arrhenius plot of permeability versus temperature data showed that there is a slope discontinuity at near to T-g of PEMA. In addition, the effects of membrane preparation parameters by solvent casting method (percentage of polymer in solvent, annealing temperature, annealing time, evaporation temperature, and evaporation time) have been investigated by using homogenous dense membranes of PEMA. It is observed that membrane preparation parameters strongly affect the membrane performance and the reproducibility of the permeability measurements. On the other hand, the effect of polymer structure on membrane performance has been investigated. Comparison of the permeabilities of N-2, Ar, O-2, CO2, and H2 gases in PEMA and PMMA membranes shows that PMMA membranes have smaller permeabilities and higher selectivities than PEMA membranes because of their higher glass transition temperature, T-g. (c) 2007 Wiley Periodicals, Inc.