The standard (p(o) = 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4-transmethoxycinnamic acids in the gaseous phase were derived from the standard molar enthalpies of combustion in oxygen of the crystalline compounds determined by static bomb combustion calorimetry at T = 298.15 K and from the literature values for the respective enthalpies of sublimation.