The stability and the structure of small silver and silver-oxide particles are investigated by a comparison between experimentally deduced intensity relations in the evaporative ensemble limit and theoretical results of a Born-Oppenheimer local spin density molecular dynamics calculation. We have found two-dimensional (2D) structures for pure small silver particles up to seven atoms and three-dimensional (3D) above. In contrast, we found 3D structures for all oxidized clusters even the small ones. Small silver cluster therefore undergo a 2D-to-3D structural transition by oxidation. The electronic shell structure of the metallic part still persists, when the oxygen atoms are added, taking into account that each oxygen atom reduces the number of valence electrons by 2. The enhanced stability at electronic shell closings presents some unusual evaporation channels like the ejection of a single oxygen atom from Ag3O+ leading to Ag3O+-->Ag-3(+)+O as the preferential decay channel. (C) 2003 American Institute of Physics.