The interfacial behaviour of two unstable binary liquid-liquid systems was investigated under normal gravitational conditions and under the microgravity conditions achieved in the NASA KC-135 parabolic flights to decouple gravitational instabilities from Marangoni instabilities. Results indicate that under normal gravitational conditions interfacial convection was observed in both systems. Under microgravity thermal Marangoni disturbances were strong enough to produce interfacial instabilities in one of the systems. Results are interpreted in terms of interactions between Marangoni and gravitational instabilities.