Successions of long gas bubbles and liquid slugs form the so-called slug flow pattern in a gas-liquid flow. A unit cell encompassing one gas bubble and one liquid slug characterizes this alternating gas-liquid flow. The kinematic and dynamic flow mechanisms responsible for the interactions between the successive unit cells are still an open question. Inside this context, this work addresses specifically to the bubble velocity, the bubble to bubble interactions and the entrance mechanisms. Within an experimental framework the spatial evolution of each unit cell structure is individualized during the acquisition period. The experimental apparatus consisted of a 23.4 m long transparent Plexiglas pipe, 26mm ID, which means a total relative length of 900 free diameters. The air and water were mixed at the inlet of the test section and discharged into a collecting tank open to the atmosphere. The instantaneous measurements of the flow structure were made with double-wire conductive probes. The probes were installed in four measuring stations; each station had two probes slightly apart. The measuring stations were located at 127D, 273D, 506D e 777D from the mixer. The experimental database is further processed to give rise to histograms and correlations among flow variables