Abstract A Pittsburgh No. 8 coal, and two IBC (Illinois Basin Coal) 101 and 112 coals were oxidized in a 2 1 Parr Stirred Bench Top Reactor. The oxidation time was varied up to 5 h; the temperature from 150°C to 225°C, the oxygen pressure from 100 to 600 psi, and coal dosage from 15 to 60 g in 600 ml of distilled water. The oxidation of coal was evaluated by measuring total acidic group formed on the coal surface as well as by measuring adsorption of calcium ion on the oxidized coal from a solution in a separate system. It was found that upon oxidation of coal, acidic groups were formed on the coal surface and were responsible for the adsorption of calcium ion. The oxidation increased with increasing oxygen pressure without much leveling-off effect. However, the oxidation increased sharply with increase in temperature from 150°C to 180°C and then tended to level off above 180°C. The optimum oxidation conditions were determined by considering BTU loss and Ca/S molar ratio where S is the total sulfur in coal. The optimum oxidation conditions of Pittsburgh No. 8 coal were 170°C and 500 psi O 2 with 60 g of coal for 3 h, while those of IBC 112 coal were 150°C and 500 psi O 2 with 60 g of coal for 3 h. Under these conditions, the Ca/S molar ratio reached approximately 1.3 and the BTU loss was less than 20%. This value of Ca/S molar ratio may be high enough to capture sulfur during fluidized combustion and coal gasification. Thus, it is concluded that the present method has the potential to be used in a commercial process for preparation of a feed stock for fluidized-bed combustion and coal gasification.