Experimental data on phase equilibria have been used for thermodynamic analysis of the iron solubility of the nickel sulfides Ni7S6 and Ni9S8. For both compounds, a two-sublattice approach within the framework of the compound energy formalism has been applied to perform Gibbs free energy modelling at 0.1 MPa total pressure consistently embedded in recent thermodynamic assessment studies of other iron-nickel-sulfides. The predicted maxima of iron solubility around 3 at% of Ni7S6 and 5.5 at% of Ni9S8 are confirmed by experimental data. The calculations of complex ternary phase relations with Fe-bearing Ni7S6 and Ni9S8 gain further improvement. The first internally consistent description of all thermodynamically stable phases known in the literature for the iron-nickel-sulfur system is completed. (C) 2010 Elsevier Ltd. All rights reserved.