Four advanced oxidation processes (UV/TiO2, UV/IO4−, UV/S2O82−, and UV/H2O2) were tested for their ability to mineralize naphthenic acids to inorganic carbon in a model oil sands process water containing high dissolved and suspended solids at pH values ranging from 8 to 12. A medium pressure mercury (Hg) lamp was used, and a Quartz immersion well surrounded the lamp. The treatment goal of 5 mg/L naphthenic acids (3.4 mg/L total organic carbon (TOC)) was achieved under four conditions: UV/S2O82− (20 mM) at pH 8 and 10, and UV/H2O2 (50 mM) at pH 8 (all with the Quartz immersion well). Values of electrical energy required to meet the treatment goal were about equal for UV/S2O82− (20 mM) and UV/H2O2 (50 mM) at pH 8, but three to four times larger for treatment by UV/S2O82− (20 mM) at pH 10. The treatment goal was also achieved using UV/S2O82− (20 mM) at pH 10 when using a Vycor filter that transmits light primarily in the mid and near UV, suggesting that that treatment of naphthenic acids by UV/S2O82− using low pressure Hg lamps may be feasible.