This paper reports the standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the gaseous phase. Delta(f)Hm(0)(g), at T = 298.15 K, of 1-(2-nitrophenyl)pyrrole and of 1-(4-nitrophenyl)pyrrole as (235.7 +/- 2.7) kJ center dot mol(-1) and (205.5 +/- 2.5) kJ center dot mol(-1), respectively. These values were derived from experimental thermodynamic parameters, namely from the standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, Delta H-f(m)0(cr), at T = 298.15 K, obtained from the standard molar enthalpies of combustion, Delta H-c(m)0, measured by static-bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature-vapour pressure dependence, obtained by the Knudsen mass loss effusion method. Additionally, the gas-phase enthalpies of formation were estimated by G3(MP2)//B3LYP calculations, using several gas-phase working reactions, and were compared with the experimental determined ones. Experimental and theoretical results are in very good agreement and show that 1-(4-nitrophenyl)pyrrole is thermodynamically more stable than the 2-isomer. This composite approach was also used to estimate the gas-phase enthalpy of formation of the 1-(3-nitrophenyl)pyrrole. (C) 2010 Elsevier Ltd. All rights reserved.