Abstract: Method of removing metals from hydrocarbon feedstock using esters of carboxylic acids, and additives for the same, are provided, wherein hydrocarbon stream including crude oil containing metals and salts thereof, wherein metal is calcium and its salt is calcium naphthenate, is mixed with an effective metal-removing-amount of an aqueous extraction-solution of non-precipitating and non-fouling additive comprising a chemical compound selected from a group consisting of methyl or ethyl or propyl or isopropyl mono- and/or di-esters of any one of the carboxylic acids selected from the groups consisting of maleic acid, maleic anhydride, and fumaric acid, or an appropriate combination of said esters, or an appropriate combination of any of said esters with any of said carboxylic acids to form a hydrocarbonous phase and an aqueous phase containing the metal ions; and separating aqueous phase.