Activity coefficients at infinite dilution have been determined for three brominated hydrocarbon water mixtures in the temperature range 298-323 K. Water-rich mixtures have been studied using a gas-liquid chromatographic apparatus and for organic-rich mixtures an isopiestic technique has been used. The results have been used to obtain UNIFAC group interaction parameters for the interactions Br/H2O, CBr/H2O, CBr2/H2O and CBr3/H2O.