This paper provides detailed comparisons of chemical reaction mechanisms of H-2 applicable at high preheat temperatures and pressures relevant to gas turbine and particularly Alstom's reheat gas turbine conditions. It is shown that the available reaction mechanisms exhibit large differences in several important elementary reaction coefficients. The reaction mechanisms are assessed by comparing ignition delay and laminar flame speed results obtained from CHEMKIN with available data, however, the amount of data at these conditions is scarce and a recommended candidate among the mechanisms can presently not be selected. Generally, the results with the GRI-Mech and Leeds mechanisms deviate from the Davis, Li, O Conaire, Konnov and San Diego mechanisms, but there are also significant deviations between the latter five mechanisms that altogether are better adapted to hydrogen. The differences in ignition delay times between the dedicated hydrogen mechanisms (6 Conaire, Li and Konnov) range from approximately a maximum factor of 2 for the H-2-air cases, to more than a factor 5 for the H-2/O-2/AR cases. The application of the computed ignition delay time to reheat burner development is briefly discussed. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.