AbstractA study was made of the abilities of the Soave and Peng‐Robinson equations to represent the phase behavior of ethane + n‐paraffin and CO2+ n‐paraffin systems. These equations are capable of describing the phase behavior of such systems; however, the level of precision obtained varies with the degree of complexity used in representing the interaction parameters in the mixing rules employed. For ethane/C02with n‐paraffins extending from C3to n‐C44, an uncertainty of about 1 % is obtained for bubble point pressures (or about 0.005 mole fraction for solubilities) when two system‐specific interaction parameters per isotherm are used. Simple generalized correlations are presented for the equation‐of‐state interaction parameters which allow prediction of the bubble point pressures with an expected uncertainty of about 5.7% (0.014 in