Thermopower and electrical conductivity data for both single crystal and polycrystalline undoped CoO are considered in terms of a defect disorder model based on doubly ionized cobalt vacancies as the predominant defects. The analysis, based on the Debye-Huckel theory for liquid electrolytes, aims at an evaluation of the interactions between defects such as doubly ionized cation vacancies. It was shown that, in the temperature range 1200-1700 K, the reciprocals of the partial pressure of oxygen p(O-2) exponent of thermopower and electrical conductivity vary between 3.6 < n(alpha) < 4.2 and 3.5 < n(sigma) < 3.8, respectively. About 1300 K, both n(alpha) and n(sigma) are higher for single crystal than for the polycrystalline specimens. It was shown that closer agreement between the defect model and experimental data can be obtained by introducing defect activities instead of concentrations.