Detailed vibrational–electronic and simplified electronic state-to-state approaches for transport properties of non-equilibrium high-temperature flows are developed using the generalized Chapman–Enskog method. The algorithm for the transport coefficients calculation takes into account variable collision diameters of excited species. Effective diameters of atoms and molecules in different electronic and vibrational states are evaluated using the Slater, Hirschfelder and Tietz-Hua models; the latter two models yield similar results for molecules at the ground electronic state. At temperatures above 10000 K, a noticeable effect of increasing collision diameters on the state-specific transport coefficients is found, especially in case of non-equilibrium distributions over internal states.