The performance of several extended surfactants as water-in-crude oil emulsion breakers was evaluated using two criteria: (1) the demulsifier dose required (C-D*) to attain the minimum stability at the so-called optimum formulation, and (2) the corresponding low minimum stability value. These surfactants were found to behave in the same way as typical commercial demulsifiers do; i.e., they require a lower dose C-D* when their hydrophilicity is slightly greater. The reported data for a dozen different extended surfactants indicate how the two performance indices are altered by changing the structure characteristics, such as the propylene oxide number, the ethylene oxide number, and the ionic polar group (carboxylate, sulfate, phosphate). The best performance as a demulsifier seems to depend on the proper combination of these structures to attain a well-fitting compromise.