Injection of fluids into subsurface reservoirs is a cause for induced earthquakes. Physics-based numerical models may help to better understand the physical processes that lead to such seismicity. Recent models mainly focused on single-phase flow, and therefore the influence of multiple phases (e.g. gas) on induced seismicity remains unclear. In order to better understand the potential influence of gas on induced earthquakes, we perform numerical simulations with TOUGH-FLAC accounting for multi-phase and multi-component fluid flow. By testing different scenarios, we are able to assess the relative contribution of the gas to the seismicity. The results show that overpressurized gas may prestress fault zones and lead to faster fault reactivation and larger fault slip and rupture area during fluid injection operations. The effect of the gas decreases with increasing reservoir depth. The results of this study contribute to a more complete understanding of the physical processes leading to induced earthquakes related to geo-energy projects.