The densities rho, speed of sound u, data of o-toluidine (i)+ tetrahydropyran (j)+ N-methylformamide (k) and its sub-binary o-toluidine (i)+ tetrahydropyran (j); tetrahydropyran U) +N-methylformamide (k); o-toluidine (i)+ N-methylformamide (k) mixtures have been measured over entire mole fraction at 298.15, 303.15 and 308.15K. The excess molar enthalpies, H(E) data of o-toluidine (i) + N-methylformamide (k); tetrahydropyran U)+N-methylformamide (k) binary mixtures have also been measured as a function of composition at 308.15 K. The densities and speeds of sound of binary and ternary mixtures have been utilized to determine their excess molar volumes, V(E) and excess isentropic compressibilities, K(S)(E). The topology of the constituents (Graph theory) has been employed to determine V(E), H(E) and K(S)(E) data of binary as well as ternary mixtures. It has been observed that the estimated excess properties compare well with their corresponding experimented values. (C) 2011 Elsevier B.V. All rights reserved.