A three-parameter cubic equation of state has been proposed for predicting PVT for polymers and VLE in polymer solutions. The pure component parameters a(ii), b(i), and c(i) for seven polymers have been correlated using the PVT data. The correlated accuracy of PVT at temperatures from 308 to 491 K and pressures up to 200 MPa is 0.05%. The solvent activities in polymer solutions have been predicted for 45 binary data sets using the excess Gibbs free energy mixing rule combined with the group solution model. The pure solvent parameters a(ii) and b(i) necessary for predicting the activities have been evaluated directly using the correlation previously generalized using the critical temperature, critical pressure and acentric factor. The total average deviation of activities is 11.10%.