AbstractGraphical correlations of binary gas diffusion coefficients are developed based on the Hirschfelder‐Bird‐Spotz diffusion equation and the theorem of corresponding states. A critical diffusion coefficient is defined and is used in turn for a definition of a “reduced” coefficient. The reduced diffusion coefficient is correlated graphically in generalized form in terms of the reduced properties of the diffusing gas. Using air as a reference “barrier” gas, the authors compared critical diffusion coefficients for various gases diffusing through a single barrier gas with the critical coefficients for these gases through air. This ratio, termed thebarrier gas ratio, was found to be independent of the properties of the diffusing gas. A graphical correlation of the barrier gas ratio enables rapid estimation of a binary diffusion coefficient with a minimum of