Gas-liquid flows inside the submerged entry nozzle (SEN) of a slab mold and its influence in the flow field in the mold were studied using video recording, mathematical simulations and particle image velocimetry (PIV) approaches. Bubbly and annular flows in the SEN yield structurally-uncoupled and structurally coupled flows in mold, respectively. High gas loads (ratio of mass flux of gas and mass flux of liquid) at high casting rates lead to increases of bubble population and bubbles sizes due to coalescence processes whose rate exceeds that of their breakup. The presence of gas bubbles or gas layers inside the SEN lead to periodical twisting of the liquid flow that induces biased flows through both ports yielding uneven flows in the mold. A multiphase mathematical model predicts acceptably well the flow dynamics of two-phase flows inside the SEN. (c) 2005 Elsevier Ltd. All rights reserved.