Originally published as:Klebingat, S., Kempka, T., Schulten, M., Azzam, R., Fernández-Steeger, T. M. (2016): Innovative thermodynamic underground coal gasification model for coupled synthesis gas quality and tar production analyses. Underground Coal Gasification, Thermodynamic model, Synthesis gas quality, Tar production, Environmental impacts 2 ABSTRACT Underground Coal Gasification (UCG) technology is steadily improving due to high scientific and industrial efforts in currently over 14 countries worldwide. A fundamental UCG objective refers to syngas production for multiple end-uses, accompanied by environmental impact mitigation focusing contaminant reduction. In terms of this topic, the control of groundwater quality endangering tars has been a key problem rarely addressed in UCG publications so far.Considering UCG main sub-processes, operating parameters and tar spectrum knowledge