Oriented (100) single crystal of titanium dioxide (rutile) was equilibrated at an ambient oxygen partial pressure p(O-2) 10(-15) to 10(5) Pa, over the temperature range 900-1400 K. After the step change of p(O-2) to a new value, the equilibration kinetics was monitored by measuring electrical conductivity. Application of the Fick's second law to the kinetic data gave the chemical (ambipolar) diffusion coefficient for both oxidation and reduction runs. The chemical diffusion coefficient D-chem was found invariant with oxygen partial pressure.