The standard (p(o) = 0.1 MPa) molar enthalpies of formation Delta(f)H(m)(o)(1 or cr) at the temperature T = 298.15 K were determined by means of combustion calorimetry for 2-ethyl-aniline, 2-iso-propyl-aniline, 2-tert-butyl-aniline, 2,6-di-methyl-aniline, 2,6-di-ethyl-aniline, 2,6-di-iso-propyl-aniline, and 2,4,6-tri-tert-butyl-aniline. The standard molar enthalpies of vaporization (or sublimation) of these compounds were obtained from the temperature dependence of the vapor pressure measured in a flow system. The resulting values of Delta(f)H(m)(o)(g) were obtained at the temperature T = 298.15 K and used to derive strain enthalpies of alkyl-anilines. The intra-molecular interactions of the substituents were discussed in terms of deviations of Delta(f)H(m)(o)(g) from group additivity rules. These values provide a further improvement on the group-contribution methodology for estimation of the thermodynamic properties of organic compounds.