Biomass torrefaction in gas atmospheres containing oxygen, such as hot flue gases or air, is an interesting concept with potentially positive implications with respect to processing costs and efficiency. This study aimed to investigate the effects of varying concentrations of oxygen in the atmosphere on the torrefaction of sugar cane bagasse in a packed bed at different temperatures under realistic conditions of direct convective heat transfer. In addition to understanding the development of bed temperature profiles, the study included an analysis of the torrefied solids (higher heating value (HHV) determination using bomb calorimetry) and the torrefaction volatiles (NDIR spectroscopy for permanent gases; HPLC with UV-vis/refractive index detection for condensates). It was observed that for this specific reactor configuration and heat transfer regime, there are temperature-specific limits beyond which an increase in oxygen concentration leads to an oxidative thermal runaway in the packed bed. An increase in the torrefaction temperature from 270 to 290 degrees C, for example, led to a reduction in the tolerable limits of oxygen concentration from 5% to 1%. It was further determined that away from the ignition zone, moderate addition of oxygen does not drastically reduce the mass and energy yields of the solids and in some cases may also lead to more uniform heating of the biomass bed. An increase in oxygen concentration also leads to a shift in the partitioning of the volatiles in favor of gaseous products, with specifically an increase in carbon dioxide, resulting in reduction of the HHV of the volatiles.