Petroleum coke-derived activated carbons were prepared and used for the adsorptive removal of a single-ring naphthenic acid (NA) from synthetic oil sands tailings pond water (TPW). The overall adsorption process was found to be intra-particle diffusion-controlled. The Weber-Morris intra-particle diffusion rate constants decreased from 7.43 to 1.23 mg/g min 0.5 after activated carbon was post-oxidized with oxygen, suggesting a hindering effect of oxygen surface groups. The Freundlich model fit of the equilibrium adsorption isotherms and the small negative ΔHo pointed to a physisorption-dominated process and the importance of specific surface area. It was estimated that about 2.7 g/L of basic CO2 -activated carbon is needed to reduce NA concentration from 120 mg/L to 2.5 mg/L (~98% removal) in synthetic TPW. However, equilibrium adsorption capacity was found to vary significantly after oxygen or nitrogen groups were introduced onto the surface. Therefore, there is a potential for enhanced adsorption by chemical functionalization of carbon.