Abstract: In a method for thermally reforming an emulsion, comprising removing water and an alkali metal or alkaline earth metal salt contained in an oil-in-water type emulsion of a tarry material or a heavy fuel oil (e.g., ORINOCO BITUMEN), sulfuric acid is added, in an amount of preferably 0.05% to 1.0% by weight based on the emulsion, to the emulsion, the mixture is allowed to stand at such a temperature as to give a difference in density between separated water and heavy fuel oil, preferably for 10 min or more, to permit oil-water separation, and the separated oil phase is withdrawn. When the tarry material is ORINOCO BITUMEN, an emulsion made of ORINOCO BITUMEN is thermochemically reformed by adding 0.1 to 0.4% by weight of sulfuric acid to ORINOCO BITUMEN, allowing the mixture to stand under pressure at a temperature of 170.degree. to 200.degree. C.