This report documents an assessment of uppermost Cretaceous to Tertiary gas resources in the interior plains of the Western Canada Sedimentary Basin. The resources are described in terms of detailed geological play analysis and numerical assessment of undiscovered gas potential using a technique termed the discovery process model, which employs the volume and discovery sequence of individual pools or plays, within a natural population of pools or plays, to predict undiscovered potential. The analysis evaluated 12 mature and 2 immature established plays, and identified one conceptual play. The geology of the plays is outlined in a manner that can be used as a guide for exploration, and each play is designated by geological formation, reservoir, or trap type.