Abstract: Metals, nitrogen and/or sulfur, particularly vanadium, nickel and nitrogen, are removed from organic compositions, particularly heavy hydrocarbon oils, by contacting the organic composition with a methylating agent, preferably dimethyl sulfate, under conditions sufficient to form a precipitate, including the contaminants, and separating the precipitate from the organic composition as by filtration, decantation, and the like. In another embodiment of the present invention, the treatment with the methylating agent is carried out in conjunction with treatment with an acid gas and water or a solvent, such as a combination of carbon dioxide and water.