Abstract A much more elegant method using three groups of solvent mixtures was employed to determine the Hansen three-dimensional solubility parameters (HSPs) of hydrogenated nitrile rubber (HNBR). The HSPs obtained by this way are comparable with previous work. The Flory-Rehner relationship was used to investigate the effects of the crosslink density and the molar volume of solvent on the swelling response of the HNBR matrix. Both of these factors have a significant effect on the swelling volume in high swelling conditions (small Ra and Mc values) while the swelling curves show the characteristic reversed S-shape. The swelling volumes of HNBR (Therban 2568) in solvents and solvent mixtures have been calculated quantitatively by the Flory-Rehner relationship and correlated with the energy difference (Ra). The calculated swelling volumes decrease with increasing Ra values and also show the characteristic reversed S-shape, which correlate well with the experimental values. Therefore, it is expected that the swelling behavior of HNBR based vulcanizates in mixed fluids, taking bio-fuels and bio-based service fluids as examples, may now be predicted quantitatively.