Emulsion stability is a fundamental determination for separation technologies. We use the critical electric field (CEF) and viscosity changes in DC electrorheological (ER) experiments in dynamic mode to establish the level of stability of water-in-crude oil emulsions previously studied through bottle tests. The CEF value corresponds to the value of electric field at which the current reaches 95% or larger of the plateau value. Our results show that CEF can be obtained through current measurements and viscosity drops resulting from emulsion structure breakdown, although viscosity changes are not always a good proxy of stability. This implies that electrorheology cannot be uncritically used for static stability determination of the CEF value. Emulsion structure breakdown is explored through rheological characterization before and after voltage sweeps have been performed. When the electric field applied is below the CEF value, the storage and loss moduli response, as well as viscosity, as functions of frequency are recovered. However, when the electric field is greater than the CEF value, the emulsion structure breaks down irreversibly.