Isobaric vapor-liquid equilibrium (VLE) data for the binary system monochloroacetic acid + dichloroacetic acid have been measured at 5,7.5. and 10 kPa. The VLE data measured in this work is thermodynamically consistent according to the Herington area method. The non-ideal behavior in the vapor phase was correlated using the Hayden-O'Connell model. Wilson, NRTL, and UNIQUAC were used to account for the liquid phase non-idealities. All activity coefficient models were able to describe the experimental VLE data very well. Wilson and UNIQUAC described the VLE data slightly better than NRTL The correlated equilibrium temperatures and vapor phase compositions were in all cases in good agreement with the experimental data. (C) 2011 Elsevier B.V. All rights reserved.