Phase behaviors of high molecular weight polyethylene solutions with hydrocarbons, halogenated hydrocarbons, and oxygen-containing hydrocarbons and their mixture as solvents were examined under high temperature and high pressure, especially near the critical and supercritical condition of the solvent. The pressure temperature (P,T) cloud point curves for polyethylene in pentane, trichlorofluoromethane, and hexane were measured at different compositions. The pressure composition (P,C) cloud point curves at 473 K are presented for three systems. The P,T cloud point curves for volume fraction, phi = 2%, of high molecular weight polyethylene were measured in different hydrocarbons and halogenated hydrocarbons. It was found that the cloud point pressures of the solutions have good correlation with the critical temperature (T(c)) of solvents. The P,T cloud point curves for phi = 2% of high molecular weight polyethylene were measured in different hydrocarbon and pentane mixtures, different halogenated hydrocarbon and pentane mixtures, and different oxygen-containing hydrocarbon and pentane mixtures at volume ratio 50/50. The P,T cloud point curves for high molecular weight polyethylene in mixed solvents of 1,1-dichloro-2,2,2-trifluoroethane (HCFC123) + cyclohexane with volume ratio of 75/25 were also measured as a function of polymer composition.