Isobaric VLE data for 1-methyl-3-ethylbenzene (1M3EB) or 1-methyl-4-ethylbenzene (1M4EB) + 1, 2, 4-trimethylbenzene (124TMB) at 20 kPa were determined with a modified Rose-Williams type recirculation still. Herington area test method was used to test the thermodynamic consistency, showing good quality. The thermodynamic models of Wilson, NRTL, and UNIQUAC were used to correlate the measured data. All the three models represented the measurements well. Positive deviation behavior was observed for the 1M3EB + 124TMB system, while negative deviation behavior was observed for the 1M4EB + 124TMB system. The information presented in the paper is essential for the design and operation of distillation columns for the separation of the mixtures. (C) 2013 Elsevier Ltd. All rights reserved.