This digital dataset represents historical geochemical and other information for 58 sample results of produced water from 56 sites in the Orcutt and Oxnard oil fields in Santa Barbara and Ventura Counties, respectively, in southern California. Produced water is a term used in the oil industry to describe water that is produced as a byproduct along with the oil and gas. The locations from which these historical samples were collected include 20 wells (12 in the Oxnard oil field and 8 in the Orcutt oil field). The top and bottom perforations are known for all except one (Dataset ID 33) of these wells. Additional sample sites include 13 storage tanks, and 13 unidentifiable sources. Two of the storage tanks (Dataset IDs 8 and 54), are associated with one and two identifiable wells, respectively. Historical samples from other storage tanks and unidentifiable sample sources may also represent pre- or post-treated composite samples of produced water from single or multiple wells. Historical sample descriptions provide further insight about the site type associated with several of the samples. Eleven sites, including one well (Dataset ID 30), are classified as "injectate" based on the sample description combined with the designated well use at the time of sample collection (WD, water disposal). Two samples collected from wells in Orcutt (Dataset IDs 4 and 7), both oil wells with known perforation intervals, and one sample from an unidentified site (Dataset ID 56) are described as zone or formation samples. Three other samples collected from two wells (Dataset ID’s 46 and 49) in Oxnard were identified as water source wells which access groundwater for use in the production of oil. The numerical water chemistry data were compiled by the U.S. Geological Survey (USGS) from scanned laboratory analysis reports available from the California Geologic Energy Management Division (CalGEM). Sample site characteristics, such as well construction details, were attributed using a combination of information provided with the scanned laboratory analysis reports and well history files from CalGEM Well Finder. The compiled data are divided into two separate data files described as follows: 1) a summary data file identifying each site by name, the site location, basic construction information, and American Petroleum Institute (API) number (for wells), the number of chemistry samples, period of record, sample description, and the geologic formation associated with the origin of the sampled water, or intended destination (formation into which water was to intended to be injected for samples labeled as injectate) of the sample; and 2) a data file of geochemistry analyses for selected water-quality indicators, major and minor ions, nutrients, and trace elements, parameter code and (or) method, reporting level, reporting level type, and supplemental notes. A data dictionary was created to describe the geochemistry data file and is provided with this data release.