This dataset contains geochemical and other information for 268 samples of produced water from the Lost Hills and North and South Belridge Oil Fields. Produced water is water coexisting with oil and gas. The historical produced water chemistry data was compiled from preexisting datasets and scanned images into a numerical dataset to characterize produced water chemical characteristics. Each sample is identified by its API (American Petroleum Institute) number, excluding the state code, which is 04 in all California wells, latitude and longitude, well name, formation name, perforation interval, and date tested. The geochemical analyses include major ions, some minor ions, total dissolved solids (TDS), pH, specific gravity, resistivity, electrical conductivity, and charge balance.