The palladium-catalyzed carbonylation of phenol to form diphenyl carbonate (DPC) requires the presence of a metal co-catalyst to catalyze the reoxidation of palladium from Pd-0 to Pd2+ in the presence of oxygen. In this study, we utilize a high throughput screening (HTS) methodology to rapidly study the nature of the co-catalyst with an emphasis on combinations of metal co-catalysts that appear to work in a synergistic manner to increase palladium usage. Critical new developments were made in using a small-scale reactor in diffusion controlled systems. The HTS system is described along with the optimized catalyst packages that were determined. Additionally, the results from HTS were used to better elucidate the mechanism of this potentially important commercial reaction. (C) 2003 Published by Elsevier Science B.V.