Superconducting oxide materials, containing Bi, Mg, Pb(Sb), Sr, Ca and Cu in various nominal stoichiometric proportions, are synthesized. The critical temperature of the samples is in the range of 90 to 96 K. The chemical and phase composition of the materials is investigated by emission spectral analysis and X-ray diffraction measurements, and the microstructure by scanning electron microscopy. It is established that the addition of magnesium results in the formation of a 15 K phase Bi2Sr2Cu1O6+β. Superconductivity is also observed at around 95 K in the Bi-Sb-Mg-Sr-Ca-Cu-O system. © 1991 Chapman & Hall.