A rotating-bomb combustion calorimeter was used to determine the standard (p degrees = 0.1 MPa) molar enthalpies of combustion, Delta H-c(m)degrees, of the liquids 2-acetyl-3-methylthiophene, 2-acetyl-4-methylthiophene, and 2-acetyl-5-methylthiophene, from which the standard molar enthalpies of formation, Delta H-f(m)degrees,, in the liquid phase, at the temperature of 298.15 K, were derived. The standard molar enthalpies of vaporization, Delta H-g(1)m degrees, at T = 298.15 K, for those compounds, were obtained by high temperature Calvet microcalorimetry. [GRAPHICS] From the experimental results, the standard molar enthalpies of formation of the three methyl substituted 2-acetylthiophene isomers, in the gaseous phase, were calculated and a comparison between the relative stability and the energetic of the three isomers was carried out. (C) 2008 Elsevier Ltd. All rights reserved.