  The rise of a single bubble confined between two vertical plates is
investigated over a wide range of Reynolds numbers. In particular, we focus on
the evolution of the bubble speed, aspect ratio and drag coefficient during the
transition from the viscous to the inertial regime. For sufficiently large
bubbles, a simple model based on power balance captures the transition for the
bubble velocity and matches all the experimental data despite strong time
variations of bubble aspect ratio at large Reynolds numbers. Surprisingly,
bubbles in the viscous regime systematically exhibit an ellipse elongated along
its direction of motion while bubbles in the inertia-dominated regime are
always flattened perpendicularly to it.
