Phase equilibria in the Me-Cu-(O) systems were studied using experimental and calculation procedures. XRD and DTA were used for experimental determination of thermodynamic data, For the calculation of the phase diagrams a mathematical solution of the equations resulting from the condition of thermodynamic equilibria in partially open systems was employed. As a result the series of phase diagrams of the SrO-CuOx, BiO1.5-CuOx and BaO-CuOx pseudobinary systems for the various partial pressures of oxygen are presented.