This U.S. Geological Survey (USGS) Data Release is focused on the geochemistry of wells within the oil zone and groundwater monitoring wells away from the oiled zone at the National Crude Oil Spill Fate and Natural Attenuation Research Site, Bemidji MN (USA) from 1985-2015. The site located in Beltrami County is where a high-pressure pipeline carrying crude oil burst in 1979 and spilled approximately 1.7 million liters (10,700 barrels) of crude oil into glacial outwash deposits. Researchers and scientists from government agencies, academic institutions, the regulatory community, and private companies have conducted extensive investigations of groundwater geochemistry in hopes of understanding the evolution of plumes and the fate of the hydrocarbons within them. Laboratory measurements of BTEX (Benzene, Toluene, Ethylbenzene, o, p, m-Xylene), Total VHC (Volatile (30) hydrocarbons), NVDOC (Non-Volatile Dissolved Organic Carbon), CH4 (methane), FeT (Iron Total), Mn2+ (Manganese), Si (Silicon), NH4+ (ammonium), AsT (Arsenic Total), Alkalinity as HCO3- (Bicarbonate), Cl (Chloride), Acetate, Formate, and Propionate (Organic Acid Anions), and Delta 13C of DIC (Dissolved Inorganic Carbon) are included in this data release. There are six files (*.xlsx and *.csv) in this dataset: 1) Data Dictionary, 2) Water/Oil Chemistry in the North and South Oil Pools in 2010, 3) Benzene/Naphthalene ratios in oil and water, 4) Selected volatile and semi-volatile aromatic hydrocarbons in the North Oil Pool (2010-2015), 5) Concentrations of Delta 13C of DIC and methane from 1985 to 2015, and 6) Concentrations of NVDOC from 1986 to 2015.