AbstractExisting data on the self‐reactions of tertiary peroxy radicalsRO2has been reanalyzed and corrected to deduce Arrhenius parameters for both termination and nontermination paths. ForR=t‐Butyl, these are logkt(M−1sec−1) = 7.1 ‐ (7.0/θ) and logknt(M−1sec−1) = 9.4 ‐ (9.0/θ), respectively, different from those recommended by other authors. The higher magnitudes observed for termination processes of tertiary peroxy radicals like those of cumyl and 1,1‐diphenylethyl have been discussed in terms of a much greater cage recombination of cumyloxy radicals as contrasted witht‐butoxy radicals. It is shown that for benzyl peroxy radicals, theR—O ˙2bond dissociation energy is sufficiently low (18–20 kcal) that reversible dissociation intoR˙+ O2opens a competing second‐order path to fast recombinationR˙+RO ˙22→ROOR. This path is probably not important for cumyl peroxy radicals under usual experimental conditions but can become important for 1,1‐diphenyl ethyl peroxy radicals at (O2)<10−3M. At very lowRO ˙2concentrations (<10−5M), in the absence of added O2, an apparent first‐order disappearance ofRO ˙2can occur reflecting the rate determining breaking of the cumyl—O ˙2bond followed by the second step above. The thermochemistry ofRO ˙nis used to show that the reaction ofR2O4→ 2RO + O2must be concerted and cannot proceed v