The mobility of one of two types of fast moving negative charge carriers was measured by a time-of-flight method over a wide range of the solvent density p in gaseous, supercritical, and liquid carbon dioxide. Charge carriers are formed by laser photoinjection into neat CO2. At low densities below 2 mol/L, the mobility decreases inversely proportional to rho(6.3). The mobility becomes minimum near the critical density and increases at higher densities. The location of the mobility minimum approximately coincides with that of the isothermal compressibility maximum. The mobility increase at higher densities is understood as the result of the onset of the hopping electron transport or of the formation of the conduction band. Both of the hopping and the equilibrium (the conduction band) models are consistent with the mobility behavior observed.