Molar excess volumes, V-E and molar excess enthalpies, H-E of binary mixtures formed by o-toluidine (i) and benzene or toluene or o- or p-or m-xylene (j) mixtures have been determined dilatometrically and calorimetrically as a function of composition at 308.15 K. The observed data have been estimated using graph theory (which in turn depends upon the topology of the constituents in pure and mixed states). Predicted values compare well with their corresponding experimental values. IR studies lend further credence to the nature and extent of interaction of the proposed structures of molecular species in these mixtures. (c) 2008 Elsevier B.V. All rights reserved.