We report the use of a new method to separate the ionic and electronic contributions to the conduction of solids that involves the use and proper interpretation of low amplitude variable frequency ac measurements. This is a relatively simple technique and has some advantages over the dc methods that are normally employed for this purpose, the Tubandt Faraday’s Law method, the dc assymetric polarization technique that is often called the Hebb–Wagner method, and the dc open circuit potential method. The temperature dependence of the transference numbers of several members of the SrSnO3 family of perovskite-like oxides, both with and without Fe substitution for some of the Sn, determined by this new method are reported.