The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board collected produced water and gas samples in the Oxnard Oil Field in Ventura County in August 2018 and the Placerita Oil Field in Los Angeles County in December 2018. Sampled sites included oil wells; injectate from tanks, pipelines, and injection wells where produced water from many wells, after removal of oil, is stored or transported prior to underground injection; and integrated produced water from many oil wells collected from pipelines before oil removal. This digital dataset contains the site information, analyzing laboratories and methods, and water and gas chemistry and quality-control results for these samples. Chemistry results include concentrations of dissolved noble and hydrocarbon gases and their isotopic composition; concentrations of inorganic constituents including salinity, major and minor ions, trace elements, and nutrients; dissolved organic carbon and optical properties of dissolved organic carbon; stable isotopes of water, strontium dissolved in water, and carbon in dissolved inorganic carbon; and radium isotopes. Samples were analyzed in the field and by eight laboratories operated or contracted by the USGS.