Excess molar enthalpies, measured at the temperature 298.15 K and atmospheric pressure conditions by means of a flow microcalorimeter, are reported for the ternary mixtures x(1)C(6)H(12) + x(2)C(4)H(8)O + (1 - x(1) - x(2)){(CH3)(3)CCH2CH3 or (CH3)(2)CHCH(CH3)(2)}. A smooth representation of the results is described and used to construct constant-enthalpy contours on a Roozeboom diagram. It is shown that good estimates of the excess molar enthalpies of the ternary systems can be obtained from the Liebermann-Fried model by using the physical properties of the components and the parameters determined from their binary mixtures. (C) 2010 Elsevier Ltd. All rights reserved.