The experimental isotherms of 2-ethyl-2-oxazoline in supercritical carbon dioxide SCO2) were reported up to a pressure and temperature of 17.48 MPa and 373.2 K, respectively. The unbroken mixture critical line starting from pure SCO2 to pure 2-ethyl-2-oxazoline with a pressure maximum suggests the type I behavior in the system. The theoretical investigation is conducted with the help of Peng-Robinson equation of state (PR EOS) and satisfactory agreement is observed between predicted and experimental results. The solubility of poly(2-ethyl-2-oxazoline) in supercritical DME (dimethyl ether) is examined experimentally which demonstrates UCST (Upper Critical Solution Temperature) phase behavior for poly(2-ethyl-2-oxazoline) concentration range from 3.9 wt% to 5.0 wt%. Furthermore, the experiments are performed to determine the effect of co-solvents on the phase behavior of poly(2-ethyl-2-oxazoline) + DME + alcohol solutions. The phase shift from UCST to LCST (Lower Critical Solution Temperature) is noted for poly(2-ethyl-2-oxazoline) + DME + alcohol (methanol and ethanol) with rising alcohol concentration. Moreover, for poly(2-ethyl-2-oxazoline) + DME + alcohol (1-propanol., 1-butanol., 1-pentanol, and 1-octanol.), UCST phase behavior is observed for all concentrations of the alcohols. The drastic depression in the cloud point curve in the presence of a medium-chain alcohols (1-propanol to 1-octanol) is probably due to the association of alcohol with the polymer molecules.