Summary Exploration play-analysis methods are designed for individual or conceptual exploration plays to assess conventional petroleum resources. Play-analysis techniques usually are applied to a small area of appraisal, such as a geologic trend comprising a series of stratigraphic traps or structural traps. Play-analysis procedures, incorporating Monte Carlo techniques, also have been applied to entire geologic horizons, formations, or stratigraphic units of a geologic basin or province. The application of exploration play-analysis techniques to broad frontier provinces for the assessment of conventional petroleum resources by the USGS are reviewed and the results for the Natl. Petroleum Reserve of Alaska (NPRA) and the William O. Douglas Arctic Wildlife Range (WODAWR) are discussed. Introduction Exploration play-analysis methods have been designed for identified or conceptual exploration plays within a basin or province in order to assess conventional petroleum resources. The basic definition of an exploration play is: A practical meaningful planning unit around which an integrated exploration program can be constructed. A play has geographic and stratigraphic limits and is confined to a formation or a group of closely related formations on the basis of lithology, depositional environment, or structural history. However, many variations of this definition and of the basic assumptions applied to play concepts have been accepted by various resource estimators when using play-analysis techniques. Play-analysis methods usually have been applied to the appraisal of relatively small areas, such as a geologic trend consisting of a reef play or a channel or a bar sand. However, the play-analysis procedure has been applied to some entire geologic horizons or stratigraphic units for the appraisal of a total basin or province--e.g. the total Cretaceous potential within a basin or the potential of an entire basin. Although the estimator may have called the procedure a "play analysis," the basic concepts are obviously no longer those of the original definition. Thus, there are some extreme variations in this method and in the respective assumptions from one estimator to another. Recently, exploration play-analysis techniques have been applied to frontier areas where geological and geophysical data are limited and the geologic variables have been described by subjectively derived probability functions based on the judgment of the estimators or by the use of selected analogs. A simulation model was designed in the U.S. Dept. of the Interior, Office of Minerals Policy and Research Analysis (DOI/OMPRA), in response to a directive resulting from the Naval Petroleum Reserves Production Act of 1976. This act required that the president of the U.S. have a study conducted to determine the best overall procedures to be used in the development, production, transportation, and distribution of any petroleum resources in the reserve and to determine the economic and environmental consequences of alternative procedures. The activities simulated by the integrated model are the exploration, development, production, transportation, and distribution activities for oil and gas on the basis of the results of the play-analysis approach in the geologic sub model. Only the geologic and exploration sub models are discussed here.