We measured the ionic conductivity of amorphous poly[oligo (oxyethylene glycol) methacrylate] (PMEO)-lithium salt complexes under a CO2 pressure varying from 0.1 to 20 MPa. The pressure dependence of the conductivity was positive, and the conductivity was higher than that under an inert gas such as N-2. The ion-conductive behavior has been modeled using both the Vogel-Tammann-Fulcher (VTF) equation and activation volume theory. The calculated parameters of the VTF equation show that CO2 that had permeated into the PMEO matrix acts as solvent molecules to dissolve ions and lower the glass transition temperature at high pressures. The ionic conduction in PMEO complexes under high-pressure CO2 was scarcely related to the VTF parameters and activation volume equations. (c) 2005 Wiley Periodicals, Inc.