Three raw fatty oils were used as precursors for demulsifiers. The hydrolyzed form of each oil was adducted with maleic anhydride then modified by esterification with polyethylene glycols or ethyleneoxide-propyleneoxide block copolymers. The demulsfication efficiency, coalescence rate, some surface active, thermodynamic properties, and partition coefficient of a selected demulsifier were investigated. The best demulsifier shows 100% demulsification after 19 minutes at 300 ppm. A correlation between demulsification efficiency and rheological properties of the investigated demulsifier was investigated. Also, emulsification kinetics were followed by microscopic photography. A mechanism following coalescence and flocculation of water droplets is proposed.