The (NiO + CaO + MgO + SiO2) system and its ternary subsystems (NiO + CaO + MgO) and (NiO + CaO + SiO2) have been studied by a combination of thermodynamic modeling and experimental measurements of phase equilibria. A complete literature review and critical evaluation of phase diagrams and thermodynamic properties of all oxide phases in these systems at 1 atm total pressure are presented. To resolve the contradictions in the literature data for the (NiO + CaO + SiO2) system, a new experimental investigation has been carried out over the temperature range from (1330 to 1500)degrees C using an equilibration and quenching technique followed by electron probe X-ray microanalysis (EPMA). The compositions of phases for equilibria among liquid, pseudo-wollastonite, clino-pyroxene, olivine and tridymite have been measured. The whole set of experimental data, including the new experimental results and previously published data, is taken into consideration in thermodynamic modeling of oxide phases and optimization of model parameters. The Modified Quasichemical Model is used for the liquid phase. The models for olivine, melilite and pyroxene solid solutions are developed within the framework of the Compound Energy Formalism. A self-consistent set of thermodynamic functions of all phases in the (NiO + CaO + MgO + SiO2) system is obtained, which reproduces all available thermodynamic and phase diagram data within experimental error limits. (C) 2015 Elsevier Ltd. All rights reserved.