Molecular dynamics (MD) simulations and electronic spectroscopy are used to investigate solvatochromism and solvation dynamics in CH3CN+CO 2 mixtures. Experimental results for the probe solute trans-4-(dimethylamino)-4'- cyanostilbene (DCS) reveal a nonlinear dependence of the solvatochromic shifts upon composition, suggesting substantial preferential solvation of DCS by CH3CN. MD simulations show that analyzing these shifts using the common assumption of spectral additivity leads to grossly exaggerated estimates of the extent of this preference. Solvation dynamics has been measured using Kerr-gated emission spectroscopy and calculated using MD simulations. Simulation-experiment comparisons offer an interpretation of the observed dynamics in terms of nonspecific preferential solvation.