Group additivity contributions are evaluated for normal and branched thiols (mercaptans), alkyl sulfides, and polysulfides on the basis of a compilation of experimental values of the infinite dilution partial molar Gibbs energy, enthalpy, and heat capacity of hydration, together with molar volumes in aqueous solution at 298.15 K and 0.1 MPa. The thermodynamic data were treated using both first- and second-order group additivity methods. Numerical values of the contributions to each of the thermodynamic properties are obtained for the following first-order S-containing groups: SH, S, S-2, and S-3 as well as for the C-SH correction for the attachment of the thiol group to the tertiary carbon atom. In the case of the second-order group contribution method, numerical values are determined for the groups C-(S)(H)(3), C-(C)(S)(H)(2), C-(C)(2)(S)(H), C-(C)(3)(S), S-(H)(C), S-(C)(2), S-(S)(C), and S-(S)(2).