A conical combustion cell was built and utilized in combustion experiments at the In Situ Combustion Research Group at the University of Calgary to investigate the effect of continuous in situ air flux drop on the dynamics of the combustion process and to identify the characteristics of the process such as extinction air flux at the time the process matures. A full scale three dimensional dry combustion experiment was conducted on a formulated core representing typical Athabasca heavy oil reservoirs. The temperature profiles, the produced combustion gases and liquids as well as the unpacked core were examined. Minimum injected air flux at the termination of the experiments was calculated to be below 9.0 sm(3)/m(2)h; gas phase combustion parameters were analyzed. It is conjectured that the formation of fuel rich condition especially in presence of water at the location of the combustion front at certain locations of the core at certain circumstances tends to prevent energy generation at the combustion front even at high air injection rates. Also, it was shown that the counter current convection/diffusion of fuel gases from the combustion front to upstream locations of the core also known as the roll cell effect adversely influences the advancement of the high temperature combustion front which in turn impacts the oil mobilization and is recovery. This study illustrates the complexity of combustion processes and signifies characteristic behavior of the process at or close to is exhaustion.