Using an O-18 implant as an internal standard allows quantitative determination of oxygen levels in sputtered samples during a depth profile analysis, in which additional oxygen may be delivered to the surface either by an oxygen flood or by using an oxygen primary ion beam. This study has evaluated O/Si ratios in silicon samples sputtered with atomic or molecular oxygen (O-16) primary ion beams at a range of energies and angles below and above the 'critical' angle for surface SiO2 formation (i.e. the angle for which the partial sputter yield of Si drops below 0.5). For each O/Si value, useful ion yields (ions detected/atom sputtered) have been determined for positive ions of Si+ and for a variety of elements implanted into the Si wafer. (C) 2004 Elsevier B.V. All rights reserved.