The results of Bednorz and Muller  and Wu and Chu  have stimulated a tremendous volume of research on ceramic superconductors [3–7]. Despite a number of other synthetic techniques, the solid state reaction remains the choice of most workers due to its simplicity [4,5,7]: CuO, Y2O3 and BaCO3 are often used in the powder synthesis of Ba2YCu3O7−x. BaO2 is known to be a useful reagent in the synthesis of compounds containing higher oxidation states of metals . Therefore, in our study of the possible role of Cu3+ in superconducting perovskites, we also use BaO2 in the solid state reaction. This paper compares reaction chemistry, material processing and material characterization using BaCO3or BaO2 in the solid state reaction. We obtain greater mass density, increased sample homogeneity, lower resistance, and improved reproducibility for material prepared using BaO2. We would like to point out that other groups have produced Ba2YCu3O7−x using BaO2 [4,7]; Calestani and Rizzoli have reported a one-step process for producing single crystals of Ba2YCu3O7−x using BaO2 .