The invention relates to field of processing hydrocarbon feedstock including crude oil, wherein metals such as calcium are removed. In the face of the rising prices of crude oil, refiners are forced to process opportunity crudes such as DOBA, which pose many problems including fouling of equipment due to certain metallic salts, such as calcium napthenate. Calcium, which cannot be removed from crude oil during normal desalting process, poses very serious problems. The invention provides method for removal of calcium, wherein crude oil is mixed, with effective metal removing amount of aqueous extraction solution of an additive comprising a chemical compound selected from a group consisting of metallic acid, maleic anhydride or fumaric acid or salts or derivatives thereof, enabling separation of hydrocarboneous phase and aqueous phase containing metal ions, in crude desalter. Only hydrocarboneous phase devoid of calcium is processed further, thereby preventing fouling of equipment.