The thermal decomposition of hydrogen peroxide (H2O2) in seven bath gases (M = He, Ar, H 2, N 2, CO, CH 4, and H 2O) has been studied by classical trajectory calculations of the collisional energy transfer processes and master equation analyses of the pressure-dependent rate constants. The energy transfer processes are modeled with the range parameter of the exponential down model and collision frequency for energy transfer. Both of the two quantities are calculated from the collisional trajectories propagated on the potential energy surfaces directly evaluated by the optimized spin-component-scaled MP2 method. The master equation calculations using these parameters were found to give reasonable descriptions of the rate constants at low pressures. The calculated relative third-body efficiencies agree well with the available experimental data for M = He, Ar, and N-2 but the efficiency calculated for M = H2O appears to be overestimated at low temperature. The calculated rate constants are represented by the limiting high-pressure rate constant of k(infinity) = 6.7 x10(14) exp(-24800 K/T) s(-1), limiting low-pressure rate constants for M = Ar and N-2 of k(0) (Ar) = 3.65 x 10(8) (T/K)(-4.691) exp(-26470 K/T) cm(3) molecule(-1) s(-1) and k(0)(N-2) = 8.21 x 10(9) (T/K)(-5.034) exp(-26600 K/T) cm(3) molecule(-1) s(-1), the center broadening factor of F-cent = 0.7 exp(- T/3400 K), and the tabulated relative third-body efficiencies. The pressure-dependent rate constants calculated for multicomponent bath gases are reasonably reproduced by the traditional linear mixture rule, whereas the mixture rule based on the reduced pressure is found to provide a more precise description. (C) 2020 The Combustion Institute. Published by Elsevier Inc. Allrights reserved.