Combined surface and in situ tar sand bitumen production

In-situ combustion of tar sand formations is improved by introducing into an unminable tar sand formation prior to initiation of in-situ combustion hydrogen sulfide produced from upgrading tar sands from a minable tar sand formation in an area proximate the area of the unminable formation. The stream of hydrogen sulfide may contain a small proportion of hydrocarbons condensible at temperature and pressure conditions of the unminable formation. The improvement is applicable to both forward and reverse in-situ combustion processes.