The equilibration kinetics of high-purity single-crystal TiO2 were monitored using measurements of electrical conductivity in the temperature range 1073-1323 K and oxygen activity, p(O-2), range 10-13 to 75 kPa. The kinetics data were used to determine the chemical diffusion coefficient (D-chem) within narrow ranges of p(O-2). There was observed a complex effect of the p(O-2) on the Dchem, which exhibits a maximum at the n-p transition. The effect of the p(O-2) on the Dchem was discussed in terms of the defect disorder and the related semiconducting properties. The activation energy of the Dchem, which also varies with the p(O-2), exhibits a maximum at p(O-2) = similar to 10(4) Pa (143 kJ/ mol).