The electrochemical underpotential deposition (UPD) of lead on Au(110) was investigated by XPS using a custom-built ultrahigh vacuum apparatus containing a chamber for electrochemical studies. A two-step deposition process for lead UPD was confirmed. A large increase in the surface concentration of oxygen was found in solutions containing lead. The presence of lead was detected on the gold surface at all potentials within the range investigated (−500 mV to 1500 mV vs. Ag/AgCl). Degradation of chlorine by x-rays was observed. The change in surface components with potential was investigated and linked to models of UPD and oxidation. The initial random deposition of lead from solution led to surface disordering.