The entropy of formation of the interface, S*, between liquid gallium and aqueous solutions of the nonspecifically adsorbed Na2SO4 was calculated from interfacial tension measurements carried out by a wholly computerized sessile drop technique. The advantages of nonisothermal conditions over isothermal conditions for a direct estimate of S* are pointed out on the basis of thermodynamic arguments. The entropy of formation of the inner layer at the gallium/water interface, as estimated at 36 degrees C upon correction for the small diffuse-layer contribution, increases monotonically with an increase in the charge density sigma(M) on the metal over the accessible charge range and is about 1 order of magnitude greater than that at the mercury/water interface at 25 degrees C. This difference in behavior is explained on the basis of the notable difference in hydrophilicity between the two metals.