The Athabasca oil sands industry produces large volumes of process water during bitumen extraction and upgrading. This water contains naphthenic acids: a complex mixture of aliphatic and alicyclic carboxylic acids that are acutely toxic to aquatic organisms. Biodegradation and ozonation were used alone and in combination to evaluate the effectiveness of these treatments for reducing naphthenic acids concentrations and removing their associated toxicity. Experiments were conducted using actual process water as well as solutions of commercially-available naphthenic acids. Established analytical methods, including GC-MS and HPLC, were employed along with a novel HPLC/QTOF-MS method. Commercial preparations were more biodegradable than oil sands naphthenic acids but both mixtures were susceptible to chemical oxidation with ozone. Extensive ozonation of process water resulted in decreased naphthenic acids concentrations and complete removal of toxicity. Partial oxidation of commercial naphthenic acids also reduced their concentration and toxicity, but did not significantly change the rate of biodegradation.