Measurements of excess molar enthalpies at the temperature T = 298.15 K in a flow microcalorimeter, are reported for the two ternary mixtures {x(1)(C5H12O or C5H10O) + x(2)cC(6)H(6) + x(3)(CH3)(2)CHCH2C(CH3)(3)} by mixing component 1 with binary mixtures of components 2 and 3. Smooth representations of the ternary results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The application of the Liebermarm and Fried model to predict ternary excess enthalpies yielded approximate but correct trend of variation with concentration and the presence of an internal maximum in both ternary systems, using only the physical properties of the components and their binary mixtures. (C) 2004 Elsevier Ltd. All rights reserved.