In this paper, effects of synthesis parameters (synthesis temperature and time) and feed pressure on CO2 and CH4 gas permeances through zeolite T membranes were investigated. Experiments were carried out at three levels of synthesis temperature: 100, 120 and 140 degrees C; synthesis time: 15, 30 and 50 It and two levels of feed pressure: 1 and 5 bar. The gas permeances versus synthesis temperature first decreased with increasing synthesis temperature from 100 up to 120 degrees C, then increased with further increasing the values of synthesis temperature. The same plots were acquired for gas permeances versus synthesis time. In the case Of CO2/CH4 ideal selectivity, reverse trends were observed. This behavior was attributed to the dual effect of increasing synthesis temperature and time on gas permeance and ideal selectivity. More zeolites were deposited and larger crystals were formed at higher synthesis temperatures and times. Formation of larger crystals accelerated the rate of zeolite layer integration, which was responsible for gas separation, in one hand and reduced the density of deposited zeolite layer on the support, due to void increase, on the other hand. Gas permeances through the membranes were in the range of 10(-11) to 10(-6) (mol/m(2) s Pa). In terms of maximizing the CO2/CH4 ideal selectivity, medium synthesis temperature and time (120 degrees C and 30 h) and low feed pressure (1 bar) were selected. Maximum gas permeances were obtained at low levels of synthesis temperature and time (100 degrees C, 15 h) and high feed pressure (5 bar). Zeolite T membranes were found as good choices for the separation Of CO2 from CH4 (C) 2007 Elsevier B.V. All rights reserved.