Shock tube experiments were performed to measure the conductivity of the plasma of detonation products for potential applications in hybrid pulse detonation engines. Detonations of hydrogen/oxygen, hydrogen/air and propane/oxygen established Chapman-Jouguet shocks. The experiments indicated that seed such as potassium carbonate did not appear to significantly increase the conductivity over the unseeded gases. The conductivity measurements were compared against values obtained assuming chemical equilibrium and found to be quite small. The reasons for this anomalous behavior were attributed to incomplete mixing of the reactants and non-uniform seed distribution.