The effect of carbon dioxide on the lower critical solution temperature (LCST) behaviors of binary polyisobutylene-n-heptane, polyethylene-n-heptane, polybutadiene-cyclohexane, and polybutadiene-toluene solutions was measured with a variable-volume view cell at temperatures from 323.15 to 503.15 K and pressures from ambient to 34 MPa. After addition of supercritical carbon dioxide, the LCEPs of these binary polymer solutions were lowered by 40 to 100 K, and the phase-transition pressures in the region of the LCST for these solutions tended to increase.