Conversion of the coal particle pack in supercritical water (SCW) was studied in the semibatch reactor under the pressure of P = 30 MPa, in the temperature range of T = 500-750 degrees C, and in the reaction time of t = 60-720 s. The experimental results were analyzed within the framework of homogeneous, nonreacted core, and random pore models. The quantitative composition of conversion products was determined. Dependences of the conversion rate on the degree of coal conversion, reaction time, and temperature were described in an assumption of the first-order reaction and Arrhenius dependence. It was found that activation energy of conversion is E = 103 kJ/mol and the pre-exponential factor is A(0) = 1.3 x 10(3.1) s(-1). It was revealed that coal gasification in SCW without oxidants is the weakly endothermic process. The addition Of CO2 into SCW decreases the conversion rate and increases the CO yield.