Recovery of petroleum products or oil from underground deposits or reservoirs

The carbonaceous residue remaining in an underground formation after recovery of the oil is treated to produce gas containing carbon-monoxide and hydrogen by igniting the formation to form a combustion front at 2000-2500 DEG F. and injecting steam or steam and air to bring the temperature down to 900 DEG F. Air is then introduced to regenerate the front, and the cycle repeated. Oil is first recovered from the formation by igniting the formation and driving the resultant combustion front through the formation by injecting water or a condensible fluid, and an oxygen-containing gas either as a mixture or as alternating slugs, the gas being supplied at the rate of 500-3000 cu. ft. per barrel of water or fluid. The formation adjacent a production well is ignited and air is supplied through an injection well and the resultant combustion front travels to the injection well from which oil may be produced. The mixture of air and water is injected into the injection well and oil is produced from the production well, a suitable hydrocarbon solvent such as kerosene may be injected prior to the injection of water. The method according to the invention may be applied to a previously waterflooded reservoir.