The sulfite oxidn. method was reinvestigated to establish a procedure for the measurement of O2 transfer coeff. (KLa). Co ion catalyzed oxidns., using buffered Na2SO3 solns., were conducted in an aerated, baffled tank which was fitted with a turbine impeller, and in a multistage, countercurrent, bubble column. An empirical procedure to change the Co ion catalyst concn. was used to det. the suitable reaction conditions for KLa measurement. In the correct Co2+ range, the oxidn. rate becomes independent of Co2+, thus permitting to establish empirically the proper operating conditions. Speed and accuracy in detg. the oxidn. rate was improved by the use of O2 anal. and mass balance procedures. Study of the catalyst induction time demonstrated that the O2 uptake rate varies with time during the 1st 20-40 min, requiring that care be taken to establish steady state conditions. Expts. with 1 and 2% carboxymethylcellulose solns. showed that the method was also applicable to these viscous systems. The dynamic electrode method was applied in the stirred tank to sulfate solns. of the results when KLa was less than the inverse electrode time const. The sulfite method gave a relative error of < 10% at high KLa. At low extents of absorption in the bubble column, the specific interfacial area (a) was measured in addn. to KLa, which permitted evaluation of the mass-transfer coeff. KL. Guidelines for the exptl. detn. of KLa are presented. [on SciFinder (R)]