Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for x(1)CH(3)(CH2)(5)CH3+x(2)C(2)H(5)C(CH3)(2)OCH3+x(3)CH(3)O(CH2)( 2)OCH3. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on a Roozeboom diagram. It is shown that good estimates of the ternary enthalpies can be obtained from the Flory theory, using only the physical properties of the components and their binary mixtures.