Particle image velocimety (PIV) was used to study the motion of a single bubble as it approached and then broke through the top surface of a two-dimensional (2D) gas-fluidized bed. A digital camera recorded the motion of individual particles; this led, via computer analysis, to a complete set of particle velocity vectors around the bubble, particularly its roof, as the bubble broke through the bed surface. These results revealed the following: (1) The vorticity around the bubble is close to zero, except for the wake region at the bottom of the bubble, justifying the use of potential flow theory to predict the bubble motion around the bubble, apart from the wake. (2) Potential flow analysis, for a cylinder moving through infinite fluid, was used to predict the particle velocities for the bubble roof as the bubble broke through the surface of the bed. There is good agreement between theory and experiment for the roof velocities. (3) The experiments suggest that bubble eruption occurs when the thickness of the roof is about three particle diameters. (4) Even after eruption, the potential flow theory gives quite a good prediction of the velocities of particles from the ruptured roof of the bubble.