Excess molar enthalpies for the ternary system {x(1) 2-methoxy-2-methylpropane (MTBE) + x(2) 1-propanol + (1 - x(1) - x(2)) nonane) and the involved binary mixture {x 1-propanol + (1 - x) nonane) have been measured at the temperature of 298.15 K and atmospheric pressure, over the whole composition range. No experimental excess enthalpy values were found in the currently avaliable literature for the ternary and binary mixtures under study in similar conditions. Values of excess molar enthalpies were measured using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The group contribution model of the UNIFAC model (in the versions of Larsen et at. and Gmehling et al.) was used to estimate ternary excess enthalpy values. Several empirical expressions for estimating ternary properties from binary results were also tested.