A tight-binding model is used to obtain the electrical conductivity for liquid metals and amorphous solids within the framework of coherent-potential approximation. Following the method developed in our previous paper, the approximated equations for averaged two-particle Green's function of a lattice-gas model are obtained with short-range order for atoms included. The corresponding equations for liquid metals and amorphous solids are reduced by taking the limit of the lattice-gas model. Since the self-consistent equations so obtained contain all single-site diagrams, they have all the properties of the coherent-potential approximation.