The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board compiled and analyzed data on evaporative water loss at produced water disposal ponds at Midway-Sunset, Buena Vista, Elk Hills, McKittrick, Cymric, South Belridge, North Belridge, and Lost Hills Oil Fields in the southwestern San Joaquin Valley (SWSJV), Kern County, California. Isotopic results for samples collected at the inlet to (influent) and within percolation and evaporation ponds (effluent) were compiled from the California State Water Resources Control Board GeoTracker database at four commercial disposal facilities (Maricopa West, Maricopa East, McKittrick 1 and 1-3, and McKittrick 1-1) at the Midway-Sunset and Cymric Oil Fields. The stable isotopic compositions of oxygen and hydrogen in water were analyzed to estimate the amount of evaporation in ponds. The calculations can be used to estimate the proportion of produced water that percolates into the subsurface near disposal sites. Datasets include the isotopic results for influent samples with almost no evaporation (influent.csv) and batch files (input.csv and output.csv) that were entered into and generated from the Hydrocalculator application by Skrzypek et al. (2015) to calculate evaporative water loss for effluent samples.