We carried out equilibrium experiments of the CO2-H2O-rhyolite system at 0.1-1.5 GPa and 850 and 1200 degrees C to examine the solubility and speciation of CO2 in high-SiO2 rhyolite (SiO2 > 76 wt%). We observed that both CO2 molecules (CO2mol) and carbonate anions (CO32-) are dissolved in the quenched rhyolitic glasses based on infrared spectroscopy. This result contrasts with the general understanding that high-SiO2 rhyolitic melt dissolves CO2mol only. The concentrations of CO2mol and CO32- were 199-9200 ppm and 58- 2100 ppm, respectively, as quantified based on the Beer-Lambert's law and newly determined extinction coefficients of 1192 +/- 130 L center dot cm(-1)center dot mol(-1) and 91 +/- 28 L center dot cm-1 center dot mol-1 for CO2mol and CO32-, respectively. The water content ranged from 2.6 to 6.1 wt%. Using the thermodynamic analysis, we calculated the partial molar volume of CO2mol to be (V) over bar (melt)(CO2mol) = 24.9 +/- 2.0 cm(3)/mol and enthalpy of dissolution to be Delta H-s/u = -22.2 +/- 6.3 kJ/mol. Changes in volume and enthalpy upon the formation reaction of CO32- were calculated to be Delta V-r = - 8.6 +/- 0.9 cm(3)/mol and Delta H-r = + 1.1 +/- 4.4 kJ/mol, respectively.