As production from mature fields is decreasing and new hydrocarbon discoveries are not enough to match the growing energy demands, finding technologies to enhance the hydrocarbons recovery plays essential rule in the oil and gas industry. Therefore, enhanced oil recovery (EOR) particularly thermal EOR is becoming an essential technique in global oil production. The thermal process involves injecting steam into reservoir to heat the oil-bearing rocks and increase the production. Meanwhile, the resulted temperature changes around the wells will change the rock mechanical state of the reservoir and its surrounding. Therefore, the problem of wellbore instability during the production will becomes more critical due to the introduction of thermal stresses in the earth system. The main objective of this study is to develop a new stability model that account for the thermal effect, which is usually not considered as an input in most of the conventional borehole stability models. The model predicts critical failure pressure of vertical wellbores during production where the steam injection is adopted and it is developed using "Mogi-Coulomb" failure criterion introduced by AL-Ajmi (2006). Mathcad program was utilized to predict formation failure pressure (i.e. critical bottom hole pressure) during steam injection. To verify the model, two Omani real cases have been simulated. The model results have shown a good match with the actual field observation. A sensitivity analysis was also conducted with typical ranges of Omani oil fields. In the sensitivity analysis, the developed model was compared with the conventional borehole stability model that neglects the thermal stresses effect. The conventional model predicts a more stable borehole while the developed model that a count for thermal stresses predicts a less stable scenario in many cases. Accordingly, the results show that the application of heating leads to a less stable formation in the production stage of the well. The newly developed model in this study allows petroleum engineers to predict formation failure pressure during steam injection. This will enhance early well management, reducing time and cost. Furthermore, the optimal well design can be established. Moreover, the developed model can be utilized for both steam flooding and cyclic steam injection during production.