AQUAFAC, a new group contribution method for estimating aqueous activity coefficients, has been applied to a large set of organic compounds. The current work introduces 27 new group values for hydrocarbon, halogen, and non-hydrogen bond donating oxygen groups. Group values (q-values) have been derived from a data set of 621 compounds representing over 1700 individual solubility values. No correction factors were used in generating the current group values. AQUAFAC was found to give acceptable results when applied to some environmentally important compounds.