Quantitative analysis of small angle neutron scattering (SANS) data from homogeneous multicomponent mixtures of supercritical carbon dioxide (scCO(2)) and two polymers is presented for the first time. The two polymers used in this study were styrene-acrylonitrile copolymer (SAN) and deuterated poly(methyl methacrylate) (dPMMA). Model polymers were used to facilitate comparisons between theory and experiment. The random phase approximation (RPA) was used to derive a simple expression to describe SANS profiles. The scCO(2)-free binary blend was studied to determine the temperature dependence of the polymer-polymer interaction parameter. scCO(2)-polymer solubility data was used to relate polymer-solvent interaction parameters. Comparisons between SANS profiles from multicomponent mixtures and the RPA expression provided an estimate of the interaction parameter between scCO(2) and PMMA, chi(13). The addition of scCO(2) at a modest pressure results in a decrease of phase separation temperature T-s by 127 K. The analysis indicates that the change in T-s is caused by an increase in chi(13) with increasing scCO(2) pressure.