This paper introduces the concept of zeolite-filled microporous mixed matrix membranes, referred to herein as ZeoTIPS membranes, and discusses their potential use for gas separations. ZcoTIPS membranes, which are formed using the thermally induced phase separation (TIPS) process, consist of zeolite particles supported in a microporous polymer matrix. ZeoTIPS membranes are designed to improve upon the performance of dense mixed matrix membranes for gas and liquid separations and to approach the performance of zeolite membranes while avoiding their drawbacks. In addition to discussing the preparation of ZeoTIPS membranes and their structure, the paper presents a model that can be used to demonstrate the potential of these membranes in gas separation applications. The model presented herein depends on the zeolite loading and the ratio of void volume to polymer volume in the membrane. The permeation characteristics inherent in each of the three membrane components are also taken into account. Predicted permeation results for oxygen/nitrogen separation using ZeoTIPS membranes formed with poly(vinyl acetate) and 4A zeolite are presented and are shown to improve significantly upon predicted dense mixed matrix membrane performance. (C) 2008 Elsevier B.V. All rights reserved.