An equilibration quenching technique was used to evaluate experimentally the phase relations in the Cu-Pb-S system between 763 and 1273 K. At 763-788 K, the formation of a ternary phase was confirmed. In addition, the thermodynamic properties of the Cu-Pb-S ternary system between 763 and 1573 K were critically assessed and optimized by the CALPHAD (CALculation of PHAse Diagrams) method, using the experimental results from this work and critically evaluated literature data. The obtained thermodynamic dataset allows the thermodynamic properties and phase equilibria in the Cu-Pb-S system to be calculated with good agreement to the experimental results. The effects of different process variables on the lead and copper distributions between the metal and matte can be calculated to improve the process control and economics. (c) 2012 Elsevier Ltd. All rights reserved.