A critical evaluation of all available thermodynamic and (solid + liquid) phase equilibrium data for the (Ca + C + O + S) system has been performed. The liquid phase was modelled using the Modified Quasichemical Model in the pair approximation. The present database reproduces the (solid + liquid) equilibria of the experimentally studied subsystems of the (Ca + C + O + S) system within the experimental error limits. Estimations of the phase equilibria of systems lacking experimental data were made. The database of thermodynamic data for all phases can be used, along with other databases and Gibbs free energy minimization software, to calculate the phase equilibria and all thermodynamic properties of (Ca + C + O + S) mixtures, which are of great importance for several industrially relevant processes. (C) 2009 Elsevier Ltd. All rights reserved.