The oil sands process-affected water (OSPW), produced in large amounts during the extraction of crude oil from oil sands, is toxic mainly due to the presence of naphthenic acids (NAs), among other constituents. Ozonation is an effective method for the removal of NAs. To provide information for better control of NAs ozonation, models based on mass balance were developed in this study to predict the concentration profiles of commercial NAs, dissolved ozone, and gaseous ozone during the process. It was found that the developed models successfully predicted the concentrations of commercial NAs and gaseous ozone. For the dissolved ozone concentration, the developed model can predict the equilibrium concentrations well. However, the actual ozone consumption was higher than that predicted by the model at the initial period of the ozonation process. This deviation possibly resulted from the inapplicability of the gas-liquid equilibrium conditions at the initial high rate stage of the reaction. In addition, the Henry's law constant and the overall mass transfer coefficient for the given system were determined experimentally. Also investigated in this study was the effects of inlet gaseous ozone concentration into the reactor on the removal of NAs and on the concentration of dissolved ozone. As expected, the increase in inlet ozone concentration enhanced the removal of NAs and increased the concentration of dissolved ozone.