Tar compounds are important components of the raw gas from the gasification of solid fuels. Unfortunately, in these kinds of processes, they represent unnecessary wastes which must be removed. The widely used method for low-temperature purification of gases from the gasification of solid fuels from tar compounds consists of syngas cooling and the use of physical methods of separating tar compounds. Modern methods consist of the decomposition of tar compounds in high temperature processes. These methods utilize thermal cracking in the absence of oxygen or oxidizing atmosphere, as well as catalytic steam or autothermal reforming of tar compounds contained in the raw synthesis gas. One apparatus which could be used as a solution for this purpose is a reactor with a porous barrier. It provides heat for the endothermic tars’ decomposition reactions through the distribution of oxygen through a porous barrier. This solution also provides increased safety by reducing the partial pressure of oxygen in the reactor. This publication presents the results of high temperature and oxygen conversion of tar model compounds (toluene, -methylnaphthalene, and their mixtures) in a model gas from coal gasification consisting of 50% CO, 25% H2, 20% CO2 , and 5% CH4. The content of the model compound was about 15 g/m3 and steam about 100 g/Nm3 in terms of dry gas. The experiments were conducted in a reactor with a porous barrier used to distribute the O2 within the interior of the reactor. Research covered a temperature range of 700–1000 °C, residence time of reactants in the reactor, 1.5 s and 3.0 s, and the addition of oxygen at 5, 10, and 20% vol. relative to the amount of process gas. The experiments have shown the increment of aromatic compounds’ decomposition rates according to increases in temperature reaching levels of loss of aromatic compounds of over 50% for 1000°C. The experiments conducted at the same temperature level (1000°C) and the same residence time (3.0 s) have shown decomposition intensification of aromatics with an increase in oxygen addition.