We applied the extended RISM integral equation theory to investigate the local solvation behavior of a naphthalene solute in a supercritical carbon dioxide solvent. A ten-site model potential for naphthalene (by Sediawan, Gupta, and Mclaughlin) and a three-site potential for carbon dioxide (by Murthy, Singer, and McDonald) were used to elucidate local orientation of the carbon dioxide solvent molecules around the solute. Important physical effects of the quadrupole of carbon dioxide as well as molecular geometry of naphthalene are, therefore, taken into account. To gain insight into preferential orientation of carbon dioxide around a naphthalene molecule in a supercritical carbon dioxide solvent, we used a novel supermolecule approach by which potential of mean force surfaces of a carbon dioxide-naphthalene pair were calculated. Effects of molecular shape of solute and solute-solvent attractive interactions on solute partial molar volume were examined. © 1996 American Chemical Society.