It is shown through measurements of interfacial rheology that the effectiveness of demulsifiers is directly correlated with short relaxation times (for viscoelastic interfaces) and lower dilational elasticities and viscosities of the oil-water interface. Short relaxation times imply that interfacial tension gradients that slow film thinning are suppressed. A reduction in interparticle interactions at the interface results in smaller dilational elasticities and viscosities as well as a decrease in the magnitude of steric hindrance.