A modified gas-translation (GT) model based on a GT mechanism was successfully applied to the pore-size evaluation and gas transport behavior analysis of microporous membranes with different pore-size distributions. Based on the gas permeation results of three microporous membranes derived from different alkoxides, the effects of activation energy and the selection of a standard gas on the pore-size evaluation were discussed in a comparative study. The presence of nano-sized defects had an important influence on the gas permeation performance of microporous membranes, depending largely on the original pore size of the membrane in question. Moreover, the gas-separation effect of the pore-size distribution in a silica membrane was theoretically studied and revealed a significant increase in gas permeance for relatively large gas species but not for small ones. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 2268-2279, 2015