This data release contains the input used and the output files interpreted in the publication "Refinement of a Regression-Based Method for Prediction of Flow-Duration Curves of Daily Streamflow in the Conterminous United States". This data release contains daily streamflow data for 1,378 streamgages in 19 study regions in the conterminous U.S. (CONUS) from October 1, 1980 through September 30, 2013 from mostly undisturbed watersheds. This data release also contains the empirical flow-duration curves (FDCs) derived from this daily streamflow data, presented as 27 quantiles ranging from 0.02 to 99.98 percent nonexceedance probabilities. Selected basin characteristics from the GAGES-II dataset (https://water.usgs.gov/lookup/getspatial?gagesII_Sept2011) were transformed to reduce skewness and to convert to a similar range of values and then used, directly or in the construction of additional variables, to fit regression equations for predicting FDCs. Basin characteristic selection and transformation was performed separately for each study region. The basin characteristics considered for use in candidate regression models are presented in their original units and as their transformed values; a table specifying the variable transformations is also provided. To each group of gaged basins in each region with one basin left out, a regression model selection procedure, with four or five binary methodological choices thus 16 or 32 methodological combinations, was applied to select the best regression model for each contiguous group of FDC quantiles (called here a “flow regime”). This data release provides the definitions of the selected flow regimes, the regression model parameters, goodness-of-fit statistics of the fitted models, and predicted FDCs for the gaged basin that was left out for the selected FDC regression models for each of the methodological combinations.