In the review, the results of research in the field of heavy crudes upgrading in the presence of water are presented, depending on water phase states at temperatures ca. 150 – 550 ºC. In this temperature region, water can be in the subcritical state (compressed hot water at T = 100 – 374 ºС and saturated water vapor pressure), in the form of supercritical fluid (T ≥ 374 ºC, P ≥ 22.1 MPa) and in the form of superheated steam (at P < saturated water vapor pressure). Features of the heavy crudes upgrading including mechanisms of water involving in reactions with hydrocarbon feedstocks and model compounds as well as features of the use of catalysts are reviewed.