Water quality was investigated from October 1980 to May 1983 in an area of abandoned coal mines in Haskell county, Oklahoma. Bedrock in the area is shale, siltstone, sandstone, and the McAlester (Stigler) and Hartshorne coals of the McAlester Formation and Hartshorne Sandstone of Pennsylvanian age. The two coal beds, upper and lower Hartshorne, associated with the Hartshorne Sandstone converge or are separated by a few feet or less of bony coal or shale in the McCurtain area. Many small faults cut the Hartshorne coal in all the McCurtain-area mines. The main avenues of water entry to and movement through the bedrock are the exposed bedding-plane openings between layers of sandstone, partings between laminae of shale, fractures and joints developed during folding and faulting laminae of shale, fractures and joints developed during folding and faulting of the brittle rocks, and openings caused by surface mining--the overburden being shattered and broken to form spoil. Water-table conditions exist in bedrock and spoil in the area. Mine pond water is in direct hydraulic connections with water in the spoil piles and the underlying Hartshorne Sandstone. Sulfate is the best indicator of the presence of coal-mine drainage in both surface and ground water in the Oklahoma coal field. Median sulfate concentrations for four sites on Mule Creek ranged from 26 to 260 milligrams per liter. Median sulfate concentrations increased with increased drainage from unreclaimed mined areas. The median sulfate concentration in Mule Creek where it drains the reclaimed area is less than one-third of that at the next site downstream where the stream begins to drain abandoned (unreclaimed) mine lands. Water from Mule Creek predominantly is a sodium sulfate type. Maximum and median values for specific conductance and concentrations of calcium, magnesium, sodium, sulfate, chloride, dissolved solids, and alkalinity increase as Mule Creek flows downstream and drains increasing areas of abandoned (unreclaimed) mining lands. Constituent concentrations in Mule Creek, except those for dissolved solids, iron, manganese, and sulfate, generally do not exceed drinking-water limits. Reclamation likely would result in decreased concentrations of dissolved solids, calcium, magnesium, sodium, sulfate, and alkalinity in Mule Creek in the vicinity of the reclaimed area. Ground water in the area is moderately hard to very hard alkaline water with a median pH of 7.2 to 7.6. It predominately is a sodium sulfate type and, except for dissolved solids, iron manganese, and sulfate, constituent concentrations generally do not exceed drinking-water limits. Ground-water quality would likely be unchanged by reclamation. The quality of water in the two mine ponds is quite similar to that of the shallow ground water in the area. Constituents in water from both ponds generally do not exceed drinking-water limits and the water quality is unlikely to be changed by reclamation in the area.