I n t r o d u c t i o n Geothermal resource assessment is the estimation of the amount of thermal energy that might be extracted from the earth and used at costs competitive with other forms of energy at a foreseeable time under reasonable assumptions of technological improvement. A regional or national resource assessment provides a framework for long- term energy policy and strategy decisions by government and industry. A resource assessment is not intended to establish specific reserve figures for short- term investment and marketing decisions, but instead to give an over all perspective at a particular time, using uniform methodology and data. The first systematic effort to estimate the geothermal resources of the United States was published in 1975 as U.S. Geological Survey Circular726 (White and Williams, eds., 1975). This assessment and a followup assessment published in 1979 as Circular 790 (Muffler, ed., 1979) focused on the quantities of geothermal energy available in regional conductive environments, igneous-re1 ated geothermal systems, hydrothermal convection systems, and geopressured- geothermal systems. Estimates were given of the thermal energy recoverable from hydrothermal convection systems at temperatures above 90?C and geopressured systems. in addition, the 1979 assessment included a compilation of data on the occurrence of low-temperature geothermal water less than 90?C (Samel, 1979), but no attempt was made to estimate the quantities of thermal energy associated with such occurrences. Low-temperature geothermal resources occur in two types of geohydrologic environments. These include hydrothermal convection systems, commonly involving upward flow of thermal water along faults in areas of above-normal heat flow, and conduction-dominated areas such as sedimentary basins where aquifers of large areal extent occur beneath at thick insulating blanket of rocks having low thermal conductivity. As discussed by Same1 (19791, low-temperature geothermal resources occur throughout the United States, with some at relatively shallow depths, and appear to have the potential for significant utilization in space heating and agriculture on a 1 to1 basis. To provide estimates of the quantities of thermal energy stored in and recoverable from low temperature reservoir s in the United States, the Geological Survey has made a new assessment based on an updated inventory of low-temperature geothermal occurrences and on the development of new methodology for estimating recoverable energy. We have been aided in this task by the data gathered under programs of many state agencies and several private contractors which are supported by the State Coupled Geothermal Program of the Department of Energy's Division of Geothermal Energy. The assessment is nearly complete; results will be published as a USGS circular in 1982. We present here an outline of the methods used and general descriptions of the results obtained.

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