Microwave diagnosis showed that the early afterglow of an oxygen plasma was controlled by ambipolar diffusion and by recombination (&agr;r), depending upon pressure (from 0.15–4.0 mm Hg), at elevated gas temperatures (up to 900°K). AtTgas=300°K attachment also seemed to be important for higher pressures (p>0.65 mm Hg). For low plasma excitation energy the measurements yielded &agr;r=2.1×10−7cm3sec−1atTgas=300°K, dropping gradually to 1.4×10−7cm3sec−1at 894°K. The plasma excitation energy had a marked effect on the apparent recombination and attachment rates which tend to indicate that vibrationally excited ions and molecules do affect these rates as has been suggested previously.