Recently developed oxygen O18 method [K. Franzreb, J. Lorincik, P. Williams, Surf. Sci. 573 (2004) 291; R. C. Sobers, K. Franzreb, P. Williams, Appl. Surf. Sci. 231 - 232 (2004) 729; P. Williams, R. C. Sobers Jr., K. Franzreb, J. Lorincik, Appl. Surf. Sci. 252 (2006) 6429] is able to quantitatively determine the flux ratio of oxygen to matrix species at dynamical SIMS sputtering. This flux ratio can be directly related to the surface oxygen concentration at dynamical sputtering -an important parameter controlling the ionization yield of emitted species. It is argued that the oxygen O18 method is a worthy step forward in gathering relevant experimental data that might eventually lead to the understanding of oxygen enhancement mechanism in SIMS. A current status of understanding of the ionization processes in SIMS is briefly discussed in terms of non-adiabatic strongly velocity dependent processes represented by the electron tunneling and bond-breaking models and in terms of electronic excitation processes represented by the surface-excitation model. (C) 2008 Elsevier B. V. All rights reserved.