The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board compiled and analyzed data for mapping groundwater salinity and characterizing aquifer systems in and near selected oil and gas fields in California. Data for the Lost Hills, North Belridge, and South Belridge oil fields include production and injection volumes, oil show data, formation pressure data, digitized borehole geophysical data, geochemical analyses of produced water samples, geological formation depths, and geophysical data associated with estimating groundwater total dissolved solids (TDS) of formation water. All data reported here are used in an accompanying interpretive manuscript. These data have been compiled from many sources and span several decades. Some of these data have been in archived scanned pages in raster format on the California Division of Oil, Gas, and Geothermal Resources (DOGGR) website, but now have been compiled into computer readable numerical data sets. Other data were created by this project. All the data compiled and analyzed are part of the California State Water Resources Control Board’s Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production and the USGS California Oil, Gas, and Groundwater (COGG) program.