The standard (p(o) = 0.1 MPa) molar enthalpies of formation Delta(f)H(m)(o)(1) at T = 298.15 K were determined by means of combustion calorimetry For benzylcyanide, alpha-methyl-benzylcyanide, alpha-ethyl-benzylcyanide, and alpha,alpha-dimethyl-benzylcyanide. The standard molar enthalpies of vaporization of these compounds were obtained from the temperature dependence of the vapor pressure measured in a flow system. Resulting values of Delta(f)H(m)(o)(g) were obtained at T = 298.15 K and used to derive strain enthalpies of benzylcyanides. The strain effects were discussed in terms of deviations of Delta(f)H(m)(o)(g) from the group additivity rules. These values provide a further improvement on the group-contribution methodology for estimation of the thermodynamic properties of organic compounds.