We measured compositions of high-pressure CO2 solutions in vapor, liquid, and supercritical phases by means of UV-Raman spectra. Our goal was to investigate whether excimer-based Raman could quantitatively determine compositions of such solutions under high-pressure conditions. Some potential problems include ( a) species that can absorb much, or all, of the UV-laser light, ( b) fluorescence that might overwhelm the Raman signal, and ( c) density gradients that would bend the laser beam. We studied two binary systems that were chosen to avoid such problems and that yielded quantitative composition analyses. These were ( a) two-phase mixtures of CO2 and n-pentane and ( b) solutions of 1,1,1,2,3,4,4,5,5,5-decafluoropentane in CO2. We suggest some changes that could increase the usefulness of the method for future applications.