Advances in the field of membrane gas separation over the past decade have encouraged the search for even better polymers and membranes for gas separation. They also have motivated studies on the relationship between the structure and the gas transport properties of different classes of polymers. Interest has recently been demonstrated in the literature in norbornene polymers with different side groups. These polymers can easily be prepared via ring-opening metathesis polymerization (ROMP) of norbornene (bicycle [2.2.1] hept-2-ene) derivatives. So far, information on the microstructure of the polymers is scarce, so little is known about the influence of stereochemistry and tacticity of the polymer on gas separation properties. In this work, we present gas permeability and selectivity data for stereoregular unsubstituted polynorbornene. It will be shown that a high order of tacticity has a positive effect on both permeation and separation results.