Underground coal gasification, as an auto thermal process, includes processes of degasification, pyrolysis, and the gasification itself. These processes occur as a result of a high temperature and the management of coal combustion during addition of gasification agent. Air, water vapor mixed with air, air or water vapor enriched with oxygen, or pure oxygen, may be used as gasification agents. Resulting gas that is extracted in this process may vary in chemical composition, so it is necessary to adjust it. That is the reason why it is necessary to develop a mathematical model of the underground gasification process prior to any operations in coal deposit, in order to obtain as much accurate prediction of the process as possible. Numerical calculation provides prediction of gas mixture’s... chemical composition, which enables calculation of gas components’ energy contents and total energy content of the gas in predicted underground coal gasification process. It is one of the main criteria in the economic assessment of underground coal gasification process. This paper, based on available data on researches in this area, provides a contribution to creation of mathematical model of underground coal gasification.