Oxygen rf glow discharges between parallel plates were numerically analyzed by using the relaxation continuum model. The result at a frequency of 13.56 MHz, sustaining voltage of 150–350 sin &ohgr;tV, pressure of 0.15–1.0 Torr, and stainless steel surface, shows that O2(a1&Dgr;g) has a number density that is an order of magnitude larger than that of atomic oxygen. The plasma density as a function of pressure has a maximum at about 0.2 Torr, and decreases with increasing pressure due to the increase in the net rate of associative detachment from O−by O2(a1&Dgr;g). The comparison between the discharges in two surface materials, stainless steel and copper, indicates that the number densities of O2(a1&Dgr;g) and atomic oxygen strongly depend on the surface loss probability, and that consequently the plasma density is also changed by replacing the surface material. ©1996 American Institute of Physics.