The U.S. Geological Survey (USGS) operates a dense network of streamgages within the Delaware River Basin (DRB) that provides near real-time and daily mean streamflow values, many of which have a decades long period of record. This long-term, historical dataset of daily mean streamflows is crucial for prediction of flows at ungaged stream reaches by means of parameter-based regression equations and can assist in informing water management and use decisions within the DRB. The USGS computed updated flow-duration exceedance probabilities for 98 current (2022) reference streamgages within the DRB with at least 10 years of record and minimally altered (nominal anthropogenic activity such as mining, diversion, or impoundment) streamflow regimes. The Make Plotting Position (MkPP; Granato, 2009) program with Weibull plotting position was used to calculate flow-duration exceedance probabilities for 21 streamflow percentiles. Percent difference comparison between these resulting flow-duration exceedances were made with observed and regression equation predicted streamflow values published by Stuckey (2016) for the 1960 through 2010 time period. A time-series trend analysis of 1979–2022 daily mean streamflows at 19 percentiles was computed using a non-parametric Mann-Kendall trend test (Hirsch and others, 2015). Associated basin characteristic raster layers that are currently used in StreamStats for the DRB, including percentage sand in soil, percentage poorly drained soils, percentage urban land use, mean annual precipitation, mean winter precipitation (December–February), and soil hydraulic conductivity, are included in this data release. Citations: Granato, G.E., 2009, Computer programs for obtaining and analyzing daily mean streamflow data from the U.S. Geological Survey National Water Information System Web Site: U.S. Geological Survey Open-File Report 2008–1362, 123 p. on CD-ROM, 5 appendixes, https://pubs.usgs.gov/publication/ofr20081362 Hirsch R.M., DeCicco L.A., 2015, User Guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R Packages for Hydrologic Data: U.S. Geological Survey Techniques and Methods 4-A10, https://pubs.usgs.gov/tm/04/a10/ Stuckey, M.H., 2016, Estimation of daily mean streamflow for ungaged stream locations in the Delaware River Basin, water years 1960–2010: U.S. Geological Survey Scientific Investigations Report 2015–5157, 42 p., http://dx.doi.org/10.3133/sir20155157