The direct reaction between phenol and oxygen in water becomes rapid above 150°C, but the thermochemistry is very unfavorable for a process involving H-atom transfer to oxygen from phenol; rate constants for this process are one thousand to one billion times slower than measured rates. An electron transfer model appears to fit the measured data much better. The Arrhenius plot of oxidation rate constants over the range 100° - 420°C is reasonably linear, suggesting that the oxidation process follows similar reaction paths over this range. However, analyses indicate significant differences among products reported at 200° and 380°- 420°C. Clearer understanding of this relatively simple process is needed to optimize hydrothermal oxidations of the complex waste streams the processes are intended to treat.