presented three-dimensional transient velocity field in the continuous phase during the formation of bubbles in a 800 m squared T-junction, using a -PIV system, and divided the bubble formation process in to three stages: growth of the bubble to fill up most of the T-junction; ex-pansion of the bubble and constriction of the bubble neck; break up of the neck. Although the transient velocity fields in the liquid phase around a gaseous thread during the bubble formation process can be measured by -PIV system, the bubble formation process is so fast that the quantified features of the gaseous thread can only be captured by a high speed camera.