A secondary recovery process for oil wet sands using underground combustion to produce a makeup effluent gas containing carbon dioxide. The effluent gas is mixed with a wet casing head gas enriched by ethane plus hydrocarbons and the mixture is injected into the reservoir at relatively low pressures to promote oil flow toward a production well. The enriched injected gas mixture reduces the oil's adhesion to the sand and promotes oil flow. The production well is maintained under a vacuum pressure so as to pull the injected mixture through the formation. The mixture is recovered and reinjected. The production well vacuum pulls ethane plus hydrocarbons from the oil at the formation face to enrich the casinghead gas.