Phenols are among the most common organic pollutants because of their toxicity even at low concentrations. The effects of the retention time and the phenol concentration on the stabilization pond efficiency in the treatment of oil refinery wastewater were the purpose of this study, and hence the input of a pilot unit was varied in terms of phenol concentrations and retention time. The following parameters have been examined, NH4+, PO4 3-, phenol, TCOD, SCOD, TBOD, SBOD and pH. The results showed that the average efficiency in the stabilization ponds varied in the ranges 71.9–91.2%, 76.4–93.3%, 68.4–91.7%, 75.9–93.7% and 77.6–98.0% for the removal of SCOD, TCOD, SBOD, TBOD and phenol, respectively. These results indicated that the phenol concentration and the retention time affected dramatically the anaerobic and facultative ponds performance, so that the system performance was significantly increased by decreasing the phenol concentration and increasing the retention time. It can be concluded that stabilization ponds show favorable performance in removing organic compounds at various phenol concentrations and high retention times; this system can be therefore used to replace rather expensive and complex systems such as active sludge.