The south coast of the Caspian Sea is being faced with oil pollution because of intensive petroleum activities in the region. Stranded tar balls on the beaches are considered as one of the evidence for oil pollution. In this study, the supersaturation of tar balls, which are collected from Caspian Sea beaches, is investigated using the anti-solvent precipitation technique. The scope of this research is the metastable zone width limit and its influence on supersaturation. Supersaturation is measured for precipitated tar ball particles within a n-hexane/methanol mixture. In general, supersaturation acts as a driving force for tar ball precipitation when the anti-solvent is added. Response surface methodology is used to evaluate the influences of vital parameters, such as anti-solvent addition rate, mixing regime, initial solute concentration, and metastable zone, on the supersaturation phenomenon, leading toward obtaining a statistical model to forecast supersaturation. In comparison of the response surface model predictions to the experimental data, a very good accuracy is noticed. Moreover, the analysis of variance (ANOVA) technique is employed to evaluate validity of the proposed model, implying that the metastability zone width has the most important effect on the supersaturation.