This paper evaluates two potential uses of spent shale for the treatment of in-situ oil shale process waters -- in-situ treatment in an abandoned retort and surface treatment by columns of spent shale. Batch and column studies were conducted using four in-situ retort waters, one gas condensate, and six spent shales. The effect of spent shale contact on the organic and inorganic carbon, conductivity, and pll of the waters was determined and related to specific surface area of the shale and retort operating conditions. These studies indicate that spent shale may be used to reduce the organic and inorganic carbon, conductivity, color and odor and to elevate the pll of retort waters and gas condensate. Spent shale reduces the inorganic carbon by 47 to 98%, the organic carbon by 7 to 66% and elevates the pll from initial levels of 8 to 9 up to 10 to 11. TOSCO 11 spent shale was the best adsorbent for organic carbon, while Lurgi and simulated in-situ spent shales achieved the highest inorganic carbon reduction.