The Preliminary Inventory of Hydropower Resources (PIHR) a preliminary product of the National Hydropower Study (NHS), was published in six (6) volumes (regions) to facilitate reproduction and distribution. The PIHR contains general as well as site-specific information on our nation's hydroelectric power potential. It gives estimates of existing, incremental and undeveloped hydropower potential by state and region and furthermore, breaks these categories down into size ranges of small-scale (.05-15 MW) intermediate (15-25 MW) and large-scale (greater than 25MW) sites. Because the inventory is a preliminary product of the NHS, it may be superseded at some future date. Conservative assumptions have been made in the screening and analysis process to avoid eliminating any potentially feasible sites. The current summary tables provide the best estimated to date, but to some degree, may overstate the actual capacity and energy which could be developed.