A play analysis method of petroleum resource assessment has been developed by the developed by the U.S. Department of the Interior and was used successfully in the evaluation of two northern Alaska frontier areas: the National Petroleum Reserve in Alaska (NPRA) and the coastal plain of the Arctic National Wildlife Refuge (ANWR). The assessment procedure entails the input of subjective probability geologic judgments into a computer, which then quickly generates a set of probabilistic resource estimates. The two assessment areas are part of the same North Slope petroleum province and are generally similar except for their size and the absence of seismic and well data for the ANWR. The 17 plays in the NPRA and the 10 in the ANWR were defined stratigraphically, with the excep ion of one tectonically defined play in the NPRA.

Our results show that although the assessment area of the NPRA (about 37,000 sq mi) is approximately ten times larger than that of the ANWR coastal plain, the undiscovered in-place oil and gas resources are estimated to be nearly the same in both areas, although pool sizes are estimated to be larger in the ANWR.

These two assessments were the first ever undertaken by the USGS using the play assessment technique, and our experience suggests that several small modifications in the method would improve its efficiency and enhance its reliability. The advantages of this method over conventional procedures include its capability to furnish a record of probabilistic geologic judgments on large amounts of data and its ease of revision and updating as new information becomes available.