This data release includes field parameters (pH and specific conductance), major ion geochemistry (B, Ba, Br, Cl, Ca, Fe, K, Li, Mg, Mn, Na, Si, SO4, Sr), total dissolved solids, specific gravity, water isotopes (delta-2H and delta-18O), and radium isotopes (226Ra and 228Ra) from produced water samples taken from petroleum wells producing from the Niobrara Formation in the Denver-Julesburg Basin, Weld County, Colorado. Additionally, gas composition and stable isotopes (delta-13C-CO2, delta-13C-C1, and delta-D-C1) from these wells are included. Major ion geochemistry, total dissolved solids, specific gravity, water isotopes, and radium isotopes were analyzed at the U.S. Geological Survey laboratories in Reston, Virginia, USA. Gas compositions were analyzed by a commercial laboratory. The data release includes four files, including one metadata file and 3 comma-separated (CSV) files.