For hydrocarbon recovery from a reservoir of bituminous sands, steam and a multi-function agent are injected into the reservoir for mobilizing bitumen in the reservoir to form a fluid comprising hydrocarbons, water and the multi-function agent. The fluid is produced from the reservoir. The multi-function agent may comprise an organic molecule that reduces viscosity of oil and the interfacial tension between oil and water or a gas or rock in the reservoir, and has a partition coefficient favoring solubility in oil over water and a partial pressure in the reservoir allowing the organic molecule to be transported with steam as a vapor. The multi-function agent may comprise a solvent for reducing viscosity of oil and a surfactant for reducing interfacial tension, where both the solvent and surfactant are transportable with steam as vapor.