The promoting effect of water in different states of aggregation on the transformation processes in oxide mixture was studied in case of BaTiO3 formation. The reaction between barium and titanium oxide was carried out in liquid, in gaseous and in supercritical water. The state of aggregation of the reaction medium had an influence on the degree of transformation of the reagents and on the characteristics of produced BaTiO3 such as the crystal size, the content of volatile impurities and sinterability. On the basis of comparative investigation it was concluded that the synthesis in supercritical water appeared to be the most effective way for production of pure fine-crystalline BaTiO3 for the ceramics preparation. (C) 2016 Elsevier B.V. All rights reserved.