The standard (p(o) = 0.1 MPa) molar enthalpy of formation of 6-propyl-2-thiouracil was derived from its standard molar energy of combustion, in oxygen, to yield CO2 (g), N-2 (g) and H2SO4 center dot 115H(2)O (I), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapor pressures as function of temperature were measured by the Knudsen effusion technique and the standard molar enthalpy of sublimation, Delta H-g(cr)m(o). at T = 298.15 K, was derived by the Clausius-Clapeyron equation. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T= 298.15 K: -(142.5 +/- 1.9) kJ mol(-1). This value was compared with estimates obtained from very accurate computational calculations using the G3 and G4 composite methods. (C) 2014 Elsevier B.V. All rights reserved.