Measurements of excess molar enthalpies at the temperature 298.15 K in a flow microcalorimeter, are reported for the two ternary mixtures {X1C4H8O + X2CH3CH2CH(CH3)CH2CH3 + (1 - X-1 - X-2)CH3(CH2)(upsilon-2)CH3} with upsilon = 8 and 10. Smooth representations of the results are described and used to construct constant-enthalpy contours on Roozeboom diagrams. It is shown that useful estimates of the ternary enthalpies can be obtained from the Liebermann-Fried model, using only the physical properties of the components and their binary mixtures. (C) 2003 Elsevier Ltd. All rights reserved.