Industrial-scale rare earth extraction is typically performed by liquid-liquid extraction with large amounts of solvents, acids and organophosphorus ligands. An alternative is to use these extractants in supercritical CO2 (SC-CO2). where the crucial operating parameter is their solubility. Different molecules with amidophosphonate backbones have been synthesized and investigated to improve their solubility in SC-CO2 and their capacity to extract cerium. The CO2-philicity of these extractants was adjusted by attaching branched or linear alkyl chains with four, six and eight carbons. Using a dynamic gravimetric setup, the solubility and cerium extraction capacity of these molecules were measured to vary from 1.56 to 2.47 47 mmol(ligand)-mol(co2)(-1) and 0.25 to 0.46 mmol(ce).mol(ligand)(-1), respectively. The two properties were correlated and in both cases the highest values were obtained with a diisobutylamine chain. Solubility measurements between 313 and 331 K and between 13 and 28 MPa shows that optimal condition is (320 K : 28 MPa). (C) 2019 Elsevier B.V. All rights reserved.