The National Crude Oil Spill Fate and Natural Attenuation Research Site is located near Bemidji, MN, USA. A high-pressure oil pipeline ruptured in 1979 releasing ~1.7 million liters of light crude oil, which sprayed over an area of ~6500 square meters and collected in topographic depressions. Approximately 75% of the spilled oil was recovered. Much of the remainder reached the water table, where it is distributed into three residual oil bodies (the north, middle, and south oil pools). Groundwater flows east-northeast toward a small lake roughly 300 m downgradient from the original spill site. Secondary reactions of sediments with byproducts from anaerobic degradation of the oil plumes cause increases in total dissolved solids, which are transported in groundwater and raise the electrical conductivity of the groundwater above background levels, presenting a potential monitoring target for electrical geophysical methods. This data release contains electromagnetic induction (EMI), ground penetrating radar (GPR), electrical resistivity tomography (ERT), and specific conductance (SpC) data collected over and within the lake where it is believed high SpC groundwater associated with degradation of the oil plume is discharging. Direct measurements of lake sediment specific conductance and temperature, as well as pore water specific conductance, are also included. The current release (ver. 3.0) contains data from 2018, 2019, and 2021. Previous versions of this data release contained only data from 2018 (version 1.0), and data from 2018 and 2019 (version 2.0). The interested user can contact Neil Terry (firstname.lastname@example.org) or the USGS Hydrogeophysics Branch to obtain a copy of the original release. A revision history is also included on this root page.