"It has been estimated that up to thirty billion barrels of oil are contained in tar sand deposits in five states (California , Kentucky, New Mexico, Texas and Utah) (1)*. The deposits in Utah alone are estimated to contain twenty eight billion barrels of oil, and may be compared to the 300 billion barrel conventional petroleum resource in the US. The U.S. Department of Energy's (DOE) Laramie Energy Research Center (LERC) initiated a program in 1971 to develop in situ thermal techniques for recovery of oil from U. S. tar sand deposits. In situ thermal recovery techniques include steam stimulation (""huff and puff""), steam flooding, forward combustion (fire- flooding) , reverse combustion, and firewater flooding. These techniques have been utilized successfully in enhanced oil recovery and may be suitable for heavy viscous bitumen found in tar sands. In forward and reverse combustion , air is injected at the injection well. The reaction between the oxygen in the air and the coke (in case of forward combustion) and/or a portion of the cracked oil (in case of reverse combustion) produces heat necessary for viscosity reduction and oil cracking. The air drive produces enough pressure gradient to displace the distilled oil and oil vapor, products of combustion, and connate water towards the production well. In forward combustion the flame front moves in the same direction as the air flow. Oil flow in the colder region ahead of the flame front could result in a plugged flow due to the increased viscosity in this region. In reverse combustion, such a problem is avoided. The flame front moves in the opposite direction of air flow and oil f lows through the region towards the production wells."