Downwell pumps offer significant advantages for the production and conversion of geothermal energy resources: suppression of scale formation caused by release of dissolved CO2, increased heat for electricity conversion in binary power systems, and greater fluid production per well. However, the failure rate of downwell pumps in tests and operations at geothermal sites in the United States has been high. As a step toward continued improvement of these pumps, Radian Corporation was asked to determine the causes of failure in earlier tests of geothermal downwell pumps. This final report presents the results of the study, documenting past and current pump development and testing programs. Data were obtained through contacts with pump suppliers and operators; no new inspection of equipment was performed. EPRI has authorized a follow-on project, RP2559, to obtain additional data from further testing. These tests will develop information for comparison of different pump types in the geothermal environment