A bifurcation behaviour of flows driven by opposing buoyancy in two vertically connected open cavities was found and investigated using flow visualization experiments, theoretical analysis and computational fluid dynamics simulations. In the theoretical analysis, the fluid in each cavity was assumed to be fully mixed. It was found that two stable fixed points exist for a certain range of strength ratios of the heat source/sink. Hysteresis phenomenon was found between the two stable steady flows. The simple theoretical analysis suggests that two Hopf bifurcations also occur. Both computational fluid dynamics simulations and flow visualization confirm the existence of two stable solutions. (c) 2006 Elsevier Ltd. All rights reserved.