[en] Today, the control and the regulation of the processes of metallurgy of metal extraction, or other kind of their chemical thermic treatment, should be based on previously well studied and defined parameters for efficient work. While projecting, new technologies or optimizing the existing ones, the scientific approach is based on the treatment of an enormous number of information and data. The chemical thermodynamics with the previous thermodynamical analysis also has a great part in this. Most often it's all about complex systems, making analysis applying the classical method assumes great work, yet the results derived from the analysis are not always clearly visible. In this scientific work, based on literature data for the necessary thermodynamical values, a thermodynamical analysis was made on the system Fe-O-Cl. When making the analysis, the program 'THERMANAL' specialized on the Institute of Extractive Metallurgy (TMF-Skopje) was used as software. With this analysis, the areas of stability of pure condensed phases in the system Fe-O-Cl, are defined, depending on the potential of the gas species at a constant temperature of 833 and 881 K, and the results are given graphically in the plain log P_Cl2 [bar] - log P_O2, [bar] and the Gibbs triangle of concentrations. (Original)