Five meso-substituted cobalt(III) corroles were examined as to their catalytic activity for the electoreduction of O-2 when coated on an edge-plane pyrolytic graphite electrode in 1.0 M HClO4. The investigated compounds are represented as (TpRPCor)Co(PPh3), where TpRPCor is the trianion of a para-substituted triphenylcorrole and R = OMe, Me, H, F, or Cl. Three electrochemical techniques, cyclic voltammetry, linear sweep voltammetry with a rotating disk electrode (RDE), and voltammetry at a rotating ring disk electrode (RRDE), were utilized to evaluate the catalytic activity of the corroles in the reduction of O-2. Cobalt corroles containing electron-withdrawing substituents were shown to be better catalysts than those having electron-donating groups on the three meso-phenyl rings of the triarylcorroles.