Pressure gradient along the column in gas chromatography leads to the decompression of the carrier gas and thus varied flow velocity that can be accounted for by the Darcy's law. By solving mathematical models such as the equilibrium dispersive (ED) and the transport models, which account for axial dispersion and mass transfer processes between mobile and stationary phases, respectively, the expressions for retention time and plate height under such nonuniform condition were obtained. As a first approximation, it is assumed that pressure gradient has little affect on the mass transfer coefficients such as axial dispersion coefficient (D) and lumped mass transfer coefficient (k(f)). It is found that, by using average flow velocity ((u) over bar) that includes the parameter of inlet-outlet pressure ratio (gamma), the expressions obtained from the transport model can be reduced to the mathematical forms of the expressions deduced by assuming uniform flow velocity. By contrast, the expressions obtained from the ED model show some differences. These results indicate the coupling effect between pressure gradient and axial dispersion. In most practical cases, retention time expressions obtained from these models are consistent due to large value of average Peclet number. The plate height accounting for axial dispersion effects will vary from 2D /(u) over bar to 2.7D /(u) over bar when gamma changes from 1 to infinity.