The standard enthalpy of formation and the enthalpy of sublimation of crystalline 2-hydroxyphenazine-di-N-oxide, at T ) 298.15 K, were determined from isoperibol static bomb combustion calorimetry and from Knudsen effusion experiments, as -76.7 ( 4.2 kJ‚mol -1 and 197 ( 5 kJ‚mol -1 , respectively. The sum of these two quantities gives the standard enthalpy of formation in the gas-phase for this compound, ∆ f H°m(g) ) 120 ( 6 kJ‚mol -1 . This value was combined with the gas-phase standard enthalpy of formation for 2-hydroxyphenazine retrieved from a group estimative method yielding the mean (N-O) bond dissociation enthalpy, in the gas-phase, for 2-hydroxyphenazine-di-N-oxide. The result obtained with this strategy is 〈DH°m (N -O)〉 ) 263 ( 4 kJ‚mol -1 , which is in excellent agreement with the B3LYP/6-311+G(2d,2p)// B3LYP/6-31G(d) computed value, 265 kJ‚mol -1 .