The electrical conductivity of single crystals of rutile was measured in the “c” and “a” directions over the temperature range 1000°–1500°C and from 1 to 10−15 atm of oxygen. Based on the excellent fit observed between the theoretically derived relation and the experimental conductivity data, the nonstoichiometric defect structure of rutile was rationalized in terms of quasi‐free electrons and both triply and quadruply ionized titanium interstitials. In addition, this equation satisfies a contribution due to impurity conduction where is proportional to a temperature dependent concentration of ionized impurities or a contribution due to intrinsic conduction where is proportional to a temperature dependent concentration of holes in the valance band.