The electrical conductivity of a Pd/CeO2 aerogel catalyst has been measured in situ during the reduction of the catalyst in H-2 and during the oxidation of propane, both carried out during programmed heating. The results can be rationalized on the basis of (i) the formation of anionic vacancies in ceria upon reduction, (ii) the subsequent electron transfer from reduced ceria to Pd, a transfer which persists during the catalytic reaction, (iii) the partial reoxidation of the surface of ceria in the presence of the reaction mixture at temperatures <523 K, and (iv) the reduction of CeO2 at the Pd-CeO2 interface by H atoms abstracted from propane chemisorbed on Pd at temperatures >523 K, this abstraction being thereby favored by the support. Attempts have been made to correlate the various conduction activation energies with corresponding surface reactions.