Strong jet flows were observed emanating from micro bubbles on a 100 μm diameter wire during subcooled nucleate boiling. The flow velocities were visualized with high-speed photography and quantified with a PIV analysis. The bubble-top jet flows were characterized by a single jet at the bubble top. Both experiments and simulations indicated that the bubble-top jet flows are induced by Marangoni effects due to temperature gradients near the wire, rather than due to condensation at the bubble top. The evaporation and condensation does, however, control the jet flow intensity. Multiple jets from a single bubble were sometimes observed on bubbles that were generally larger than the heater wire. The jets were driven by the Marangoni flow at cool regions on the bubble sides resulting from upward flow of subcooled liquid. Bubble-top jet flow