Spillage and improper disposal of saline produced water from oil wells has caused environmental damage at thousands of sites in the United States. In order to improve understanding of the fate and transport of contaminants at these sites, the U.S. Geological Survey carried out multidisciplinary investigations at two oil production sites near Skiatook Lake, Oklahoma. As a part of this effort, the hydrology and subsurface transport of brine at OSPER site “A”, a tank battery and pit complex that was abandoned in 1973, was investigated. Based on data from 41 new boreholes that were cored and completed with monitoring wells, a large (∼200m×200m×20m) plume of saline ground water was mapped. The main dissolved species are Na and Cl, with TDS in the plume ranging as high as 30,000mg/L. Analysis of the high barometric efficiency of the wells indicated a confined aquifer response. Well-slug tests indicated the hydraulic conductivity is low (0.3–7.0cm/day). Simplified flow and transport modeling supports the following conceptual model: (1) prior to the produced water releases, recharge was generally low (∼1cm/a); (2) in ∼60 a of oil production enough saline produced water in pits leaked into the subsurface to create the plume; (3) following abandonment of the site in 1973 and filling of Skiatook Reservoir in the mid-1980s, recharge and lateral flow of water through the plume returned to low values; (4) as a result, spreading of the brine plume caused by mixing with fresh ground water recharge, as well as natural attenuation, are very slow.