The stability of water-in-oil emulsions formed during oil slicks or petroleum production operations is ensured by natural surfactant molecules (principally asphaltenes) that are present in the crude oil. These persistent emulsions may be broken by adding a suitable demulsifier at the proper concentration to attain a so-called optimum formulation at which the emulsion has the minimum stability. In this work, a new formulation for demulsifier has been developed which is more suitable for demulsification of heavy crude oil than the other formulations which are used nowadays. The factors affecting the demulsification are discussed, and the final formulation regardless of its price is achieved. The results confirm that the best single demulsifiers are those which cause a minimum in the interfacial tension of water and heavy crude oil. Composite demulsifier screening was used to analyze the best mixture of single demulsifiers which possess the best efficiency at water separation from heavy crude oil.