We have taken a systematic approach for interpreting X-ray photoemission spectroscopy data for passivated silver nanoparticles, and for the first time we have been able to determine the effects of nanoparticle size and of the nanoparticle stabilizers on the observed binding energies of Ag core electrons. The binding energy of Ag 3d(5/2) core electrons was found to increase with decreasing nanoparticle size. (C) 2003 Elsevier B.V. All rights reserved.