Abstract The solubilities of liquid mixtures of 10-undecenoic acid + methyl 10-undecenoate, and 10-undecenoic acid + methyl ricinoleate in SCCO2 were determined at T = 313–333 K and P = 10–18 MPa. The selectivity is higher towards methyl 10-undecenoate in a mixture of 10-undecenoic acid + methyl 10-undecenoate, whereas the selectivity is higher towards 10-undecenoic acid in a mixture of 10-undecenoic acid + methyl ricinoleate. A new model was developed based on the solution theory coupled with regular solution theory. The absolute average relative deviation (AARD%) obtained using the new model for the system of 10-undecenoic acid + methyl 10-undecenoate was 10.5 and 9.10 for the 10-undecenoic acid and methyl 10-undecenoate, respectively, whereas for the system of 10-undecenoic acid + methyl ricinoleate, the AARD% was 4.71 and 4.91 for the 10-undecenoic acid and methyl ricinoleate, respectively. These AARDs were significantly lower than the existing models indicating utility of the new model.