Eskihisar open pit mine, located at Yatagan, southwest Turkey, produces thermal coal for a power generating plant. As mining of strips advanced southwards, instability appeared to be highly critical due to the movements in the southeast wall slopes adjacent to the state highway running parallel to the pit boundary. This situation called for an immediate response to initiate a detailed geotechnical investigation program and to redesign the pit slopes. This paper outlines the most probable mode and mechanism of instability along the southeast wall, as well as field and laboratory studies, results of back analysis, discussion of the data requirements, and results of slope stability analyses performed to ensure adequate overall stability. The studies revealed that the most critical failures may occur along two or three planar surfaces, by combination of fault, bedding plane, and localized strata steepening adjacent to the fault. in multiplanar failure mode controlled by faulted blocks. The stability is sensitive to changes in length of the lower part of the basal sliding surface, as well as to the configuration and shear strength of black and highly plastic underclay. The effects of a buttress of intact rock and slope flattening on the stability are compared and discussed.