Pressure-composition isotherms have been derived from relationships obtained between electrode potential and hydrogen content for a series of Pd+Ag alloys at 25°C. For contents exceeding ca. 30 % Ag, the isotherms are supercritical in form with respect to regions of α- and β-phase coexistence; and confirm that the form of the relationship between hydrogen solubility and silver content is markedly dependent on the reference pressure.