In cooperation with the California State Water Resources Control Board Oil and Gas Regional Groundwater Monitoring Program the U.S. Geological Survey collected and analyzed groundwater and associated quality control (QC) samples to assess regional groundwater quality overlying and adjacent to the Orcutt Oil Field during September 2017 through March 2018. Groundwater samples were collected from 15 groundwater monitoring, irrigation and production wells located within a three-mile buffer zone overlying and surrounding the Orcutt Oil Field administrative boundary in Santa Barbara County, California. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds, naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon, low molecular weight organic acids, dissolved standard and hydrocarbon gases, and dissolved noble and atmospheric gases. In total, 294 constituents and water-quality indicators were measured. QC samples including replicates; source-solution, equipment, and field blanks; laboratory spikes; and split samples for interlab comparisons were collected at approximately 10 percent of the wells and results are summarized in this data release. A data dictionary was created to describe the data tables and is provided with this data release. Please refer to this data dictionary file called COGG_Data_Dictionary_OrcuttGW for definitions of fields within these data files.