This paper reports the values of the standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, Delta H-r(m)degrees(g), at T = 298.15 K, of 2,5-dimethylthiophene and 3-acetyl-2,5-dimethylthiophene as (50.6 +/- 1.9) kJ . mol(-1) and -(123.2 +/- 2.7) kJ . mol(-1), respectively. These values were derived from experimental thermodynamic parameters, namely, the standard molar enthalpies of formation, in the liquid phase, Delta H-r degrees(m) (l), at T = 298.15 K, obtained from the standard molar enthalpies of combustion, Delta H-c degrees(m), measured by rotating bomb combustion calorimetry, and from the standard molar enthalpies of vaporization, Delta H-g(l)m degrees, at T = 298.15 K, measured by high temperature Calvet microcalorimetry. The results are interpreted in terms of enthalpic increments, molecular structure and compared with structurally similar compounds. (C) 2008 Elsevier Ltd. All rights reserved.