Measurements of excess molar enthalpies at the temperature 298.15 K in a flow microcalorimeter, are reported for the ternary mixtures [x(l){CH3(CH2)(3)}(2)O+ x(2)(CH3)(3)CCH2CH(CH3)(2)+(1-x(l)-x(2))CH3(CH2)(v)CH3] where v=5 and 6. 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.