Storage requirements for various levels of streamflow regulation in the 22 major regions of the contiguous United States are presented to supersede those given in Committee Print 32 of the Select Committee on National Water Resources, U. S. Senate. At high levels of development, the storage required to provide the desired flow in 95 and 98% of the years is substantially larger than that previously given. Carry‐over storage requirements based on probability routing of annual discharge are combined with seasonal storage requirements to give the revised storage requirements, which are then used to compute revised evaporation losses and revised cost estimates by the methods previously used. The maximum net flow that could be made available for the 22 regions for 98% of the years is shown to be 965 billion gallons per day (bgd) for which a storage capacity of 3.6 billion acre‐feet would be required. A net flow of 922 bgd could be made available with 2 billion acre‐feet of storage. Any increment of flow above the 922 bgd figure would have storage costs exceeding 10 cents per thousand gallons delivered.