The kinetics of the water gas shift reaction was studied under noncatalytic conditions in supercritical water at CO/H2O ratios of 0.03 and at temperatures from 653 to 713 K. The selectivities of CO2 and hydrogen were almost equal and did not change with pressure at 673 K. The increase of pressure and water density sensitively promoted the reaction at 653 K from 25 to 30 MPa whereas the pressure and water density did not seem to affect the rate constant at 673 K from 10 to 30 MPa. The first order rate constant for CO conversion was k = 10(5.58+/-1.38) exp(-1.16 +/- 0.19 x 10(5)/RT) /s at 10-59.6 MPa and 653-866 K. (C) 2003 Elsevier B.V. All rights reserved.