Recovery of hydrocarbons from a subterranean hydrocarbon-bearing calcareous formation is effected by injecting into the formation via an injection well a dilute aqueous solution of hydrochloric acid and displacing the acid through the formation by injecting an aqueous medium which may comprise dilute hydrochloric acid wherein the acid reacts with the calcareous constituents of the formation thereby generating carbon dioxide and improving the permeability and the porosity of the formation leading to the improved recovery of hydrocarbons therefrom.