Air and ammonia gas are introduced into a subterranean formation during the in-situ combustion to increase the mobility of hydrocarbons in a subterranean formation and facilitate recovery of the hydrocarbons from the subterranean formation. The air supports in-situ combustion of a portion of the hydrocarbon within the subterranean formation to form water and establish a combustion front. The ammonia gas contacts the hydrocarbons ahead of the combustion front and reacts in-situ with naphthenic acid in the hydrocarbon to form a surfactant. The hydrocarbons, water and surfactant then form an oil-in-water emulsion that drains more freely through the formation. A production well, in fluid communication with the hydrocarbons ahead of the combustion front, may be used to remove the oil-in-water emulsion from the subterranean formation.