In this study, screening of major chemical reactions used for numerical simulations on in-situ combustion (ISC) process has been investigated to produce bitumen from oil sands reservoir. Bitumen productions from oil sands reservoirs have been successfully carried out using thermal method, such as Steam Assisted Gravity Drainage (SAGD), but operation cost including water treatment has been a big issue to continue the bitumen production. ISC has been expected to provide high recovery, low cost and saving water. However, combustion chemical reactions and their kinetic parameters for bitumen have not been completely fixed. Some numerical simulations on the combustion tube experiments with Athabasca bitumen were conducted to construct the chemical reactions. But, screening to pick up major chemical reactions is necessary to carry out a field size reservoir simulation by reducing of CPU processing time with less number of the chemical reactions. In this study, it was confirmed that the model presented Yang and Gates (2009) could simulate the experimental results of combustion tube test better than other models. Three major reactions, defined as low temperature oxidation and high temperature oxidation (LTO and HTO), were screened based on numerical simulations by extracting a reaction one by one from the model consists eight reactions. The field scale 3D numerical simulation on THAI (Toe-to-Heel Air Injection) process, an expected ISC technology to produce bitumen, has been carried out successfully for a typical oil sands reservoir by using the three reactions. Furthermore, the comparisons of numerical simulation results have been conducted between THAI and SAGD methods.