Reactions between carbon and oxygen plays an important role in metallurgical processes, where the first one is used as a fuel or (and) as a reductant. In this work, thermodynamic analysis of the carbon-oxygen system is made, taking into account two reactions: C+1/2O2=CO and C+O2=CO2. The system C–O is divided into three subsystems – C-CO, CO-CO2, CO2-O2 – and calculations of changes in gibbs free energy, enthalpy and entropy of each subsystem as function of composition in the temperature range 500-2500 K are made. Evaluation of influence of enthalpy and entropy factors on change in gibbs free energy of the system is given. The thermodynamic analysis of system carbon (graphite) – oxygen on the basis of the calculated values of change of thermodynamic characteristics is carried out. It is established that the enthalpy factor has the maximum impact on values of changes of energy of gibbs of the system in the field of structures answering to carbon oxide (IV), and entropy – in the field of structures, answering to carbon oxide (II). It is shown that the received results can be used in the analysis of the phenomena of burning and gasification of carboniferous fuel, processes of receiving cast iron and iron.