Abstract: A process to recover hydrocarbons from a hydrocarbon reservoir, namely bitumen (API<10; in situ viscosity >100,000 c.p.), said process comprising; establishing a horizontal production well in said reservoir; separately injecting an oxygen-containing gas and steam into the hydrocarbon reservoir continuously to cause heated hydrocarbons and water to drain, by gravity, to the horizontal production well, the ratio of oxygen/steam injectant gases being controlled in the range from 0.05 to 1.00 (v/v). removing non-condensable combustion gases from at least one separate vent-gas well, which is established in the reservoir to avoid undesirable pressures in the reservoir.