A process to recover hydrocarbons from a hydrocarbon reservoir, namely bitumen (API 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.