Cloud-point and coexistence pressures, sub-and supercritical, are determined experimentally for a series of ethylene and propylene solutions of nearly monodisperse and polydisperse poly(ethylene-co-propylene), referred to as PEP. The cloud-point and coexistence pressures are found to be close for solutions of nearly monodisperse PEP polymers but not for solutions of polydisperse PEP. The SAFT parameters derived from the experimental cloud points for nearly monodisperse solutes alone are found to predict the cloud-point pressures and solubilities far polydisperse PEP as well.