Oscillations of the electric potential and of the interfacial tension were simultaneously recorded in a water-oil-water system (cetyltrimethylammonium bromide (CTAB) in water/picric acid in dichloromethane/water). Both types of oscillations were perfectly correlated in time and shape. In each oscillatory cycle, the fast jumps in the electric potential are related to a rapid adsorption of the surfactant at the interface while the slow motion relaxations correspond to the liberation of the interface from the surfactant by the formation of hydrophobic cetyltrimethylammonium picrate ion pairs that diffuse into the CH2Cl2 phase. The fast inflow of CTAB to the interface is probably caused by periodically occurring convective Marangoni instabilities. The transitions to the convective regime are assumed to be controlled by the fractional surfactant coverage of the interface.