Supercritical and slightly sub critical carbon dioxide is an excellent solvent can be used to extract phenol from wastewater because it is compatible with environmental procedure, which is extremely important. The objective of this study is the assessment of the feasibility of the extraction process utilizing a near critical carbon dioxide, which would be speeded up if it is possible to predict mutual solubility data. The use of equations of state or empirical correlations for collating and predicting liquid-liquid and liquid-dense fluid equilibria depend on critical constants properties (which are not easy to obtain) and therefore, would be for the prediction of solubility related vapor phase only. It is concluded that estimation of the required parameters for these calculations would be difficult if the solute (heavy component contaminate) is a complex substance with little known information of the structural formula. An alternative procedure will be to calculate the activity coefficient from the regular solution equations which are applied to each phase. Calculations along these lines are described and the physical basis for applying these methods under the relevant conditions discussed. The regular solution theory approach in particular has been found to be encouraging for the calculations mutual solubility for heavy component contaminates particularly substances sensitive to temperature. It was also concluded that interaction parameters for the prediction of activity coefficients depended on pressure.