Technology of arc surfacing using flux cored wire, in which tungsten oxide (WO3) and aluminum are used as fillers, is of interest for practical application in order to save tungsten. Thermodynamic estimation of probability of 14 reactions between them under standard conditions was carried out using tabular thermodynamic data of reagents in temperature range 1500  –  3500  K. This interval includes temperature at the drop surface on the electrode at time of separation, so are temperatures at the arc periphery and in the upper layers of surfacing bath. The following states were considered as standard states for reagents: WO3(solid), WO3(liquid), WO3(gas); Al(ref), Al(liquid), Al(gas), Al2(gas), and as possible reaction products and standard states for them: W(ref), W(liquid), W(gas), Al2O3(solid), W; Al2O3(liquid), AlO(gas), AlO2(gas), Al2O(gas), Al2O2(gas). Reduction reactions of the oxide were recorded at 1 mole O2 . Probability of reactions was evaluated using standard Gibbs energy of reactions. Calculations were carried out in four stages. Aggregate states of oxide, metal and structure of aluminum vapor, in which oxide and metal have the greatest chemical affinity for each other were established on the first and second stages. At the third and fourth stages, the most probable state was determined for metallic tungsten and the most probable composition, and aggregate state of aluminum oxide formed as a result of alumothermy of Al2O3(solid, liquid); Al2O3(liquid); AlO(gas); AlO2(gas); Al2O(gas); Al2O2(gas). According to Al – W system state diagram, there are a number of intermediates between tungsten and aluminum: W2Al, WAl3 , WAl4 , WAl5 , WAl7 , WAl12 ; however, a search for thermodynamic properties for them shows that data are available only on melting pattern (congruent or in-congruent) and temperature of transformation. No other thermodynamic data. At the same time, based on results of our previous work on restoration of tungsten oxide by carbon and silicon, it can be predicted that aluminides of a free-frame will necessarily be formed. Performed thermodynamic analysis shows that presence in flux-cored wire used for surfacing, along with tungsten oxide WO3as an aluminum reducing agent, will necessarily lead to occurrence of reduction reactions with formation of tungsten aluminides, and possibly tungsten itself. Tungsten oxide has the highest reactivity, being in state of WO3(gas). Aluminum itself has the highest chemical affinity for WO3(gas) in form of Al2(gas) and Al(gas). Al2O(gas) appears most likely as an oxidation product of aluminum.