Low-melting paraffin wax was successfully used as a phlegmatizing agent to perform semi-micro oxygen bomb calorimetry of spectroscopically pure samples of the sensitive explosive peroxides TATP and DADP. The energies of combustion (?cU) were measured and the standard enthalpies of formation (?fH degrees) were derived using the CODATA values for the standard enthalpies of formation of the combustion products. Whilst the measured ?fH degrees of DADP (?fH degrees=-598.5 +/- 39.7 kJ?mol-1) could not be compared to any existing literature value, the measured ?fH degrees value of TATP (?fH degrees=+151.4 +/- 32.7 kJ?mol-1) did not correlate well with the only existing experimental value and confirmed that TATP is an endothermic cyclic peroxide.