The solid solubility of pure 3,5-dinitrobenzoic acid (3,5-DNBA) and 3-nitrobenzoic acid (m-NBA) and their equal-weight mixture in supercritical carbon dioxide (SCCO2) was measured using a flow-type apparatus at 308, 318, and 328 K and in the pressure range of 10.0-21.0 MPa. The solubility enhancement SE of mixed 3,5-DNBA and m-NBA in the ternary system has been observed. The mixture separation factor mu and the separation efficiency HE were investigated. A modified Kumar-Johnston (K-J) model was proposed for correlating the solubility of solid compounds in SCCO2. The experimental solubility data of pure and mixed solutes in SCCO2 were successful to be correlated by Chrastil model, the modified Adachi-Lu model, K-J model and new proposed model. Solubility data from 23 different solid compounds were taken from literature. The accuracy of the proposed model was evaluated by correlating 13 binary systems, 13 ternary systems, and 1 quaternary system. The modified K-J model satisfactorily correlated the experimental results for the solubility of all these compounds in SCCO2 within 5.11% AARD. (C) 2011 Elsevier B.V. All rights reserved.