Nine of commercially available organic peroxides were assessed with differential scanning calorimeter (DSC) and adiabatic calorimeters. These organic peroxides are cumene hydroperoxide (CHP), di-tert-butyl peroxide (DTBP) methyl-ethyl-ketone peroxide (MEKPO), tert-butyl hydroperoxide (TBHP), benzoyl peroxide (BPO), hydrogen peroxide, lauroyl peroxide (LPO), tertbutyl peroxybenzoate (TBPBZ), and dicumyl peroxide (DCPO). Exothermic onset temperatures, self-beat temperature and pressure rates, and beats of decomposition were measured and assessed. Adiabatic runaway reaction characteristics were determined by using ARC (accelerating rate calorimeter) and VSP2 (vent sizing package). Incompatibility, tests with several potential contaminants, was made using DSC VSP2, and micro-calorimeter. An incompatibility rating was developed using onset temperature, lowering of the onset temperature, beat of decomposition, maximum self-beat rate, adiabatic temperature rise, maximum pressure of decomposition, and maximum, pressure rising rate, etc. (c) 2008 American Institute of Chemical Engineers.