A symposium on resource assessment methodologies, organized by the Canadian Gas Potential Committee in Calgary, Alberta, Canada, last April 10-12, 2002 highlighted the need for ongoing research in resource assessment. Methodologies used by the U.S. Geological Survey and the Canadian Gas Potential Committee can produce significantly different results; for example, estimates for Canadian plays by the U.S. Geological Survey were only 20% of the volume estimated by the Canadian Gas Potential Committee. Key issues in assessment of exploration plays established by discoveries include determination of the underlying distribution of hydrocarbon pool or field sizes and use of economic cutoffs. For conceptual plays where no discoveries have been made, the most critical issue involves the correct appraisal of exploration risk to be applied. Future directions for assessment in established plays include the application of iterative history matching in discovery process models and Bayesian analyses. For conceptual plays, postmortem studies of both successful and unsuccessful exploration ventures are required to calibrate exploration-risk parameters. Nonconventional hydrocarbon accumulations typically contain large volumes of in-place hydrocarbons. Assessment of such plays primarily involves engineering evaluation of the volumes of hydrocarbons that can be economically recovered. A future meeting on assessment methodology is planned for 2004. The establishment of test sites where good-quality play data may be evaluated using a variety of assessment methodologies is planned.