A study of the effect of a short-chain branching distribution (SCBD) on the phase behavior of linear low density polyethylene (LLDPE) was conducted. The perturbed chain-SAFT equation of state was the underlying thermodynamic model chosen for the study; the branched polyolefins were described using a simple modeling concept previously proposed by Dominik and Chapman.(1) To isolate the effect of the SCBD on phase behavior, the copolymer systems were considered monodisperse in molecular weight. The study revealed that, in the case of low to moderate values of the polydispersity index of the SCBD, the compositional polydispersity affected the phase behavior at low polymer concentrations only. When the polydispersity index of the SCBD is high, or, in other words, when the difference in branch content between the components of the distribution is significant, additional phases appear. The formation of multiple phases results from the incompatibility of branched and linear polymers. Similar observations were made on the basis of experimental studies in the case of polymer blends. The SCBD of LLDPE was determined by the chemistry of the polymerization reaction. A broad SCBD was found to significantly affect the phase behavior of LLDPE solutions.