Knowledge of the magnitude and frequency of low flows is important for the optimal development of surface-water resources in Puerto Rico. This report presents analyses of low-flow data for 9 continuous-record gaging stations and 105 partial-record stations in southern and western Puerto Rico. The report includes analyses of lowflow data and tabulations of computed low-flow magnitude and frequency characteristics for 7-, 14-, 30-, 60-, and 90-consecutive days with recurrence intervals of 2 and 10 years for continuous-record gaging stations based on the log-Pearson Type III frequency distribution or graphically adjusted logPearson frequency curves. Estimates of low-flow characteristics are provided for partial-record stations for 7-, 14-, and 30-consecutive days with recurrence intervals of 2 and 10 years. Low-flow characteristics at partial-record stations were estimated based on the relation of base-flow discharge measurements at the partial-record stations and concurrent discharges at nearby continuous-record stations.