This digital data set contains total dissolved solids (either reported or calculated from specific conductance in lieu of reported total dissolved solids data), well construction, and well identifying information for 1,131 petroleum wells and 3,546 water wells used to map salinity in and around 31 southern and central California oil fields. The data set also includes ancillary data in the form of top perforation (petroleum wells), bottom perforation, well depth, or hole depth (water wells), land-surface elevation at the well head, and well location and identifier information. For petroleum wells missing top perforation depth (3 percent), the median top perforation depth for all wells within the field having top of perforation depth is provided as an approximation for the purpose of vertical plotting. For water wells, well depth or hole depth were used in lieu of bottom perforation depth. For water wells lacking bottom perforation, well depth, and hole depth (40 percent), the bottom perforation was estimated based on screen length when available (5 percent), or the median bottom perforation or median well depth for all wells associated with an individual field is provided as an approximation for the purpose of vertical plotting (35 percent).