Method of removing metals from hydrocarbon feedstock using esters of carboxylic acids, comprising the steps of: a) mixing hydrocarbon stream containing metals and salts thereof, wherein metal is calcium and its salt is calcium naphthenate, 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:- i) methyl or ethyl or propyl or isopropyl mono-ester of any one of the carboxylic acids selected from the group consisting of maleic acid, maleic anhydride and fumaric acid, and ii) methyl or ethyl or propyl or isopropyl di-ester of any one of the carboxylic acids selected from the group consisting of maleic acid, maleic anhydride and fumaric acid, or iii) an appropriate combination of said esters, and iv) 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; b) permitting formation of said aqueous phase and said hydrocarboneous phase, wherein said aqueous phase includes ionic water - soluble metal - acid complex of the calcium salt of said additive; c) separating or permitting to separate by themselves said two phases in a crude desalter, or by using any of conventional processes of separation; d) removing the separated aqueous phase of step (c), containing said metal - acid complex; e) processing the separated hydrocarboneous phase of step (c) by downstream hydrocarbon processing technique; wherein the contact time between said aqueous - extraction - solution and said hydrocarbon stream during the mixing action of step (a) is in the range from two seconds to six hours, preferably from five seconds to two hours; wherein the temperature in said desalter is in the range from 93°C to 163°C; and wherein the weight percentage of the dosage of said chemical compound ranges from 0.001 to 5 of weight of said desalter - wash- water. a) mixing hydrocarbon stream containing metals and salts thereof, wherein metal is calcium and its salt is calcium naphthenate, 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:- i) methyl or ethyl or propyl or isopropyl mono-ester of any one of the carboxylic acids selected from the group consisting of maleic acid, maleic anhydride and fumaric acid, and ii) methyl or ethyl or propyl or isopropyl di-ester of any one of the carboxylic acids selected from the group consisting of maleic acid, maleic anhydride and fumaric acid, or iii) an appropriate combination of said esters, and iv) 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; i) methyl or ethyl or propyl or isopropyl mono-ester of any one of the carboxylic acids selected from the group consisting of maleic acid, maleic anhydride and fumaric acid, and ii) methyl or ethyl or propyl or isopropyl di-ester of any one of the carboxylic acids selected from the group consisting of maleic acid, maleic anhydride and fumaric acid, or iii) an appropriate combination of said esters, and iv) an appropriate combination of any of said esters with any of said carboxylic acids, b) permitting formation of said aqueous phase and said hydrocarboneous phase, wherein said aqueous phase includes ionic water - soluble metal - acid complex of the calcium salt of said additive; c) separating or permitting to separate by themselves said two phases in a crude desalter, or by using any of conventional processes of separation; d) removing the separated aqueous phase of step (c), containing said metal - acid complex; e) processing the separated hydrocarboneous phase of step (c) by downstream hydrocarbon processing technique;