The estimates of existing, incremental, and the undeveloped hydropower potential for all states in the various regions of the country are presented. In the Pacific Southwest region, the maximum physical potential for all sites exceeds 33,000 MW of capacity with an estimated average annual energy greater than 85,000 GWH. By comparison, these values represent about 6% of the total potential capacity and hydroelectric energy generation estimated for the entire US. Of the total capacity estimated for the region, 9900 MW has been installed. The remainder (23,200 MW) is the maximum which could be developed by upgrading and expanding existing projects (6000 MW) and by installing new hydroelectric power capacity at all potentially feasible, undeveloped sites (17,200 MW). Small-scale facilities account for less than 4% of the region's total installed capacity, but another 600 MW could be added to these and other small water resource projects. In addition, 600 MW could be installed at potentially feasible, undeveloped small-scale sites. The small-scale resource varies considerably, with the states of California and Utah having the largest potential for incremental development at existing projects in the Pacific Southwest region. States comprising the Southwest are Arizona, California, Hawaii, Nevada, and Utah.