Forming part of the scientific project entitled "Study on Physical Properties of Mixtures Hydrocarbon + Alcohol + Ether Like Alternative Fuels", the present article reports experimental data of excess molar enthalpies for the ternary system {x(1) 2-methoxy-2-methylpropane (MTBE) + x(2) ethanol + (1 - x(1) - x(2)) nonane} and the involved binary mixture {x ethanol + (1 - x) nonane} 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 available literature for the ternary mixture under study. 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 excess molar enthalpies for the binary and ternary system are positive over the whole range of composition. The binary mixture {x ethanol + (1 - x) nonane} is asymmetric, with its maximum displaced toward a high mole fraction of nonane. The ternary contribution is also positive, and the representation is asymmetric.