A simple theoretical treatment of conduction in solids shows that apparent electron transport numbers determined by different experimental techniques are not identical. The techniques considered for stabilized zirconia were oxygen‐transfer measurements and emf measurements on galvanic cells having oxygen at two different activities at the electrodes. Transport numbers for stabilizing cations can be determined by measuring compositional changes that result from passage of an electric current through the electrolyte. The principal current carrier in stabilized zirconia is known to be the oxide ion. The apparent electron transport number in an yttria‐stabilized zirconia at 900°ndash;1100°C is found to be ≤0.005 in an oxidizing atmosphere and ≤0.011 in a reducing atmosphere. The apparent transport number for yttrium ions is found to .