A dc glow discharge at atmospheric pressure is struck at the surface of a liquid. If this dc voltage exceeds a critical value, flashover occurs, resulting in a short circuit of the liquid. Curves of time to flashover as a function of applied voltage for different liquid resistivities are given. For low resistivities, the curves show a progressive decrease as voltage is raised. For higher resistivities a discontinuity is observed which results in a sudden l0x reduction in time to flashover for a given voltage value. We propose the existence of two different mechanisms governing flashover, corresponding to both parts of the curve. One of these mechanisms is identified as the action of an electrostatic force on the discharge. The second mechanism is probably a breakdown phenomenon.