An experimental study investigated how freely rising ellipsoidal bubbles approach each other, make contact and coalesce or breakup. Pulsed planar swarms of 10-20 bubbles with Eotvos numbers from 6.0 to 27.5 were released simultaneously in aqueous solutions of 0-48 wt% sugar with Morton numbers from 3.2 x 10(-11) to 3.7 x 10(-6). Bubble interaction was recorded by a video camera following the rising bubbles. Essentially, all coalescence and breakup events occurred after, not during, wake-induced collisions by a complex process related to the bubble vortex shedding cycle. This same process was also found in multi-bubble clusters and may account for excess turbulent kinetic energy generation in bubbly flow.