In CF4 based discharges admixed with oxygen the density of CF2 radicals decreases with an increase in the oxygen flow at a fixed CF4 flow and pressure. This decrease is attributed to the increased reaction of CF2 radicals and O atoms in the bulk plasma and to the O-2 dilution effect. By taking into account these two factors the behavior of the densities of CF2 radicals, F and O atoms in CF4/O-2, discharges was theoretically investigated in terms of oxygen flow using a simple plasma chemistry model. The data provided by Buchmann et al. [J. Appl. Phys. 67 (1990) 3635] were interpreted based on the proposed model, and the validity of the model was discussed. (C) 2003 Elsevier Science B.V. All rights reserved.