The original purpose of this study was to examine the midterm projections of oil and gas production generated by the 1979 version of the Department of Energy's Midterm Oil and Gas Supply Modeling System (MOGSMS) for the 1979 Annual Report to Congress.q These forecasts applied to conventional oil and gas, onshore and offshore, in the lower 48 states from 1985 to 1995, inclusive. The specific objective of the work was to quantify the sensitivity of these projections to potential uncertainty in some of the model's key elements. But more generally, this exercise is viewed as but one good example of how to estimate the uncertainty in forecasts coming from a large computer-based model.