Monolith catalyst reactors are used for controlling emissions of automotive and industrial pollutants. Various external mass transfer correlations are available for small-pitch catalysts typical of automotive applications; however, little information is available for catalysts having larger pitch and length that are more typical of power plant applications. The present paper proposes a new correlation Sh = 2.696[1 + 0.139ScRe(d/L)](0.81) based on data for the mass transfer limited performance for the CO oxidation reaction in square-channeled titania-silica honeycomb catalysts. The correlation is suitable for describing the performance of square-channeled honeycomb catalysts used for the selective catalytic removal of nitric oxide from power plant effluents. The differences between the present correlation and other literature correlations are discussed.