Information is presented on the quantity of water transferred from one river basin to another in the western conterminous United States. The information is needed by water system managers and planners to develop water budgets for major river basins, to examine the relative extent of existing interbasin transfers, and to define the importance of transferring water to meet regional water demands. All or parts of 11 major water resources regions and 111 complete subregions comprise the study area; water is exported from 39 of these subregions. The average quantity of water exported annually during 1973-82 was about 12 million acre-feet. (USGS)