The phase relations in the BaO-TiO2-delta system within the concentration range of 14-65 mol% BaO under reducing conditions were investigated using high temperature DTA and X-ray powder diffraction. The stable compounds under these conditions were determined, together with the temperatures of the invariant reactions and the liquidus boundaries. The phase relations in this BaO-TiO2-Ti2O3 system under elevated temperatures and reducing atmospheres are represented in the form of quasi-binary phase diagrams. (C) 2003 Elsevier Science Ltd. All rights reserved.