An Institute-wide study, organized under the MIT Energy Initiative, is being conducted of the potential future role of U.S. natural gas. Prominent in this assessment is analysis of various categories of gas resources and of their supply costs considering potential technical change in production methods. The MIT Emissions Prediction and Policy Analysis (EPPA) model is being applied to analysis of the energy system implications of various levels of possible technical achievement, in the context of alternative assumptions about the stringency of greenhouse-gas control policy.