A new method for obtaining UNIFAC group-group interaction parameters is proposed using evaluated thermophysical property data generated at the Thermodynamics Research Center (TRC) of the National Institute of Standards and Technology (NIST). Using the proposed method, two sets of UNIFAC group-group interaction parameters for 52 main groups are produced based on published vapor-liquid equilibrium (VLE), excess enthalpies, and activity coefficients at infinite dilution critically evaluated on-demand with the NIST ThermoData Engine (TDE) software. The new regression analysis method includes the use of evaluated uncertainties in assessment of quality factors evaluated on the basis of consistency tests for VLE data. Validity and effectiveness of the proposed method are discussed. (C) 2011 Published by Elsevier B.V.