Abstract Sensitivity analysis of free-volume theory para­meters have been done in ternary polymer-solvent-solvent systems. Two ternary polymer-solvent-solvent systems have been studied: poly(styrene)-tetrahydrofuran-p-xylene and poly(methyl methacrylate)-ethylbenzene-tetrahydrofuran systems. Simulation analysis has been done to see the effect of all parameters involved in predicting the self-diffusion coefficient in polymer-solvent systems. Sensitivity analysis showed that the predictions are highly sensitive to ξ13 and ξ23 and, therefore, they need to be predicted with good accuracy and these two are not pure component properties.