Enhanced oil recovery from a crude oil reservoir is promoted following primary oil production, by subjecting the reservoir to water flooding, discontinuing the water flooding, preferably when the remaining oil is at an OIP level above 0.10, and then subjecting the reservoir to fireflooding with gas having an O.sub.2 content of at least 50%, preferably above 85%.

Viscous petroleum may be recovered from viscous petroleum-containing formations such as tar sand deposits in a process employing steam and air or a free oxygen-containing gas in the ratio of 0.05 to 0.65 M.S.C.F. per bbl. and a cyclical injection-production program in which first steam or steam and air are injected and fluids are produced without restriction until live steam is produced at the production well, after which steam and air are injected and production throttled to a value less than 50% and preferably less than 20% until the formation pressure at the production well rises to a value between about 60% to 95% of the steam injection pressure, after which fluid production is permitted without restriction and steam and air injection is reduced to a value less than 50% and preferably less than 20% of the original injection rate. The process should be applied to a formation in which adequate communication exists or in which a communication path is first established. The air and steam in the optimum ratio cause a low temperature, controlled-oxidation reaction in the formation. Optimum results are obtained if the pressurization and drawdown cycles are initiated shortly after the beginning of the steam-air injection program, and the process results in substantially increased oil recovery efficiency at all values of steam pore volumes injected.

Oil is recovered from an oil-bearing reservoir in a process employing an in-situ combustion process utilizing a combustion-supporting gas containing at least 75% by volume pure oxygen, and preferably substantially pure oxygen, and a sequence in which the production well or wells are cyclically throttled. In place of using an in-situ combustion process, mixtures of steam and carbon dioxide or mixtures of steam and low molecular weight C.sub.3 -C.sub.8 hydrocarbons are injected into the reservoir and the production well is cyclically throttled. The production well flow rate is restricted until the bottom-hole pressure of the well has increased to an amount of about 30% to about 90% of the fluid injection pressure at the injection well. Thereafter, the production well is opened and oil is recovered therefrom as the bottom-hole pressure declines. The throttled production cycle may be repeated at appropriate intervals during the process.

A fluid injection induced oil recovery process wherein fluid is injected into a formation via a plurality of fluid injection wells and is produced from the formation via a plurality of production wells, and excessive flow and channeling through a "thief" region between one injection well and one production well is controlled by successively (1) shutting in the one injection well and operating the one production well for a first period of time and (2) operating the injection well and shutting in the production well for a second period of time. This sequence is repeated as many times as desired. The sequence can be modified by adding the additional step of (3) operating both wells for a third period of time. This alternative sequence is also repeated as many times as desired.

An in-situ combustion method for oil recovery from a subterranean oil-bearing formation traversed by a plurality of wells comprising a series of well pattern units wherein air permeability is established sequentially in the individual well pattern units pior to the initiation of in-situ combustion, thereby resulting in an increase in overall sweep efficiency.