We have calculated the structure and the interfacial tension of microemulsions on the phase inversion path, using a single-order parameter Landau theory. We show that the observed scaling behavior of the interfacial tensions [T. Sottmann and R. Strey, J. Chem. Phys. 106, 8606 (1997)] is described by a simple theoretical model based on the assumption that the ratio of the length scales characterizing microemulsions is a universal function of the reduced temperature, on the phase inversion path. This assumption is based on the results of small angle neutron scattering experiments on this series of systems, at the optimal microemulsion temperature [T. Sottman, R. Strey, and S.-H. Chen, J. Chem. Phys. 106, 6483 (1997)] and on the scaling properties of the Landau free energy on the phase inversion path.