An unusual black water has been observed flowing from shallow wells drilled in a comparatively small area in the northern Green River Basin. Since 1949, 18 boreholes have encountered this black water, made black by organic acids dissolved in a sodium carbonate solution. Because the black water occurs in association with Green River Formation oil shale, and because we encountered a black water flow during the drilling of a corehole designed to evaluated oil-shale deposits, the Bureau has accumulated the information currently available on the black water. This paper presents a history of black water observations, describes the geology of the occurrences of black water, discusses the nature of the water, and presents a possible explanation for its origin. Interpretation of the limited data probably creates more questions than it answers, and further study should be undertaken as additional data become available.