Mass and electrical transport properties were measured in pure, single crystal Co1-xO with 0.003 less-than-or-equal-to x less-than-or-equal-to 0.044.. Electrical conductivity and thermopower were measured at temperatures from 1000°C to 1200°C in a range of oxygen partial pressures, P(O2), of 0.21 to 32 atm. The cation tracer diffusion coefficient was measured at 1200°C in the same pressure range, and at 3.7 atm. from 1064°C to 1200°C. Electrical properties were used to locate the Co1-xO/Co3O4 phase boundary. All properties show P(O2)  dependencies which are higher those that are predicted by ideal point defect theory. Analysis of the temperature dependence of hole mobility produced an activation energy for small polaron hopping of 0.37± 0.04 eV. Using this conduction mechanism, it was shown that the P(O2) dependence for stoichiometry could not be modeled using the generalized cluster approach. That is, no combination of isolated vacancies and charged vacancy-interstitial aggregates could fit the properties. A Debye-Huckel theory model was used to describe electrostatic interactions of isolated doubly charged vacancies. Although this model fits the data below 1 atm., it fails to predict the increasing dependence at pressures from 1 to 35 atm. A model was developed which considers non-interacting isolated vacancies, V' and V", and 4:1'" clusters with Debye-Huckel interactions. All properties were accurately fit from 10 -6 less-than-or-equal-to P(O2) less-than-or-equal-to 35 atm. at 1200 °C with this model.