The electronic conductivity of Nb-doped SrTiO3 single crystals, SrTi1-xNbxO3 (x=0.01, 0.001, 0.0002), was measured by a DC four terminal method in various oxygen partial pressures from 1 to 10(-20) bar at temperatures between 573 and 1723 K. The mobility of electrons and the equilibrium constant for oxygen vacancy formation were estimated from the oxygen partial pressure and the temperature dependence of the conductivity assuming a defect equilibrium among e', h center dot, V-O(center dot center dot) and Nb-Ti(center dot). The temperature dependences of the conductivity and that of the estimated electron mobility were apparently metallic with - 1.5 power dependence on temperature. Thus, the conduction mechanism of Nb-doped srTiO(3) single crystal was interpreted by the band conduction with phonon scattering. The enthalpy for oxygen vacancy formation in the bulk of Nb-doped SrTiO3 was 6.1-6.2 eV, which was almost independent of the dopant concentration. (C) 2008 Elsevier B.V. All rights reserved.