For investigations of the defect chemistry and the transport properties of oxides conductivity measurements as a function of oxygen partial pressure and temperature are commonly applied. While precise temperature control with an accuracy better than +/- 0.1 degreesC can easily be realised, stable oxygen partial pressures, e.g. between about 10(-5) and 10(-16) bar at T= 700 degreesC, cannot be achieved in a gas stream by simple gas mixing methods. We constructed an electrochemical cell consisting of a tube of platinum-coated yttria-stabilised zirconia (YSZ), a miniaturised oxygen sensor positioned close to the sample within the YSZ-tube and an electronic process controller enabling the precise adjustment of oxygen partial pressures stable for more than 24 h between log(p(O2)/bar) = 0 and 109(p(O2)/bar) = -20. The device was tested by conductivity measurements on Fe-doped SrTiO3 (0.1 mol% Fe). (C) 2004 Elsevier B.V. All rights reserved.