New derivatives of (meso-alpha,alpha,alpha,alpha-tetrakis(o-pivalamidophenyl)porphinato)cobalt (CoPs) were characterized by oxygen-binding equilibrium and rate constants of the cobalt centered in the porphyrins. They depended on the structure of the porphyrin; for example, the rate constants of oxygen binding and dissociation (k(on) and k(off)) for (alpha(3) beta-CoP4P (Chart 1) were 3 and 20 times as large as those for alpha(4)-CoB4P, respectively. Oxygen transport through the polymer membranes containing CoPs as the fixed oxygen carriers was facilitated and was affected by the oxygen-binding character or the structure of CoPs. The logarithmically linear correlation of the oxygen-dissociation rate constant of CoPs (k(off) = (3-66) X 10(3) s(-1)) with the diffusion constant of oxygen via CoPs fixed in the membranes (D-cc = (3-140) x 10(-9) cm(2) s(-1)) was given for those six CoP derivatives.