The solubilities of dibutylhydrogen phosphonate (DBHP) and dihexylhydrogen phosphonate (DHHP) in supercritical carbon dioxide were determined at 313-333 K and 10-20 MPa. The mole fraction solubility of DBHP and DHHP are in the range of 3.4 x 10(-4) to 66.4 x 10(-4) and 4.5 x 10(-4) to 806.6 x 10(-4,) respectively. The solubility data are self-consistent with Mendez-Teja model. The experimental solubilities were correlated using Chrastil, Hezave-Lashkarbolooki and three models based on activity coefficient models. Hezave-Lashkarbolooki model resulted in better solubility predictions for DBHP with an AARD of 5%. Chrastil and van Laar activity coefficient based model correlated the solubility of DHHP with a lowest AARD of 11%.