We have measured W 4f 7/2 core-level photoemission spectra from W(110) in the presence of Ni overlayers, from ∼0.2 to ∼3 monolayers. Interfacial core-level shifts associated with first-layer Ni phases have been identified: −230 ± 15 meV for the 1×1 pseudomorphic phase and −70 ± 7 meV for the 7×1 close-packed commensurate phase. At higher Ni coverages the interfacial core-level shift is −100 ± 10 meV. These shifts are analyzed using the partial-shift model of Nilsson et al. [Phys. Rev. B 38 (1988) 10357]; the analysis indicates that the difference in binding energies between the 1×1 and 7×1 phases has a large contribution from structural differences between the two phases.