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- ...