We measured the rates of carbonyl sulfide (OCS) oxidation by hydrogen peroxide H2O2 (HP) and peroxymonosulfuric acid HOOSO2OH (PSA) in 13.5-18.0 M (76-96 wt %) sulfuric acid (SA) between 290 and 306 K. The reaction is first order in both [OCS] and [peroxide], having nearly identical second-order rate constants k(1) for HP or PSA as oxidants. k(1) increases exponentially with Hammett acidity H-o, in the range investigated: log(k(1)/M-1 s(-1)) = - (9.57 +/- 0.41) -(0.80+/- 0.05) H-o , (H-o < 0),at 306 K. OCS is, however, inert toward HP in concentrated perchloric acid at equivalent no values. We infer that OCS oxidation by HP in SA proceeds by an acid-catalyzed process involving the intermediacy of PSA rather than H3O2+. k(1) depends on temperature according to log(k(1)/M-1 s(-1)) = (6.64+/- 1.58) - (2606 +/- 472)/T, in 18 M SA. The observed kinetic behavior and parameters are typical of sulfide oxidations by PSA in very acidic media. Present data, in conjunction with data on ambient HP and sulfate aerosol levels in the lower stratosphere, lead to reaction Lifetimes that are many orders of magnitude longer than the currently estimated OCS atmospheric residence time of about 4 years.