Quantitative information about adhesion and segregation energies in metallic systems can be obtained by means of the binding energy shifts between different layers observed in core-level photoelectron spectroscopy. Layer-dependent Al2p core-level spectra for Al deposited on Mo(110) are presented. The difference in adhesion energy of Al and Si on Mo is found to be 0.24 eV per atom, with the Si-Mo bonding being the stronger one. It is found that the energetics favour a segregation of Si impurities in the Al layer to the Al/Mo interface. These results are shown to be in good agreement with calculations based on Miedema's scheme.