The incipience of two-phase flow in discharging branches, from a stratified gas-liquid region, has major implications in industrial applications where safety is of primary concern. The transition from single phase liquid to a two phase gas-liquid mixture is termed the onset of gas entrainment, and may be formed by either vortex or vortex-free mechanisms. The two phase flow quality in the discharging branch is greatly impacted by vortex-free gas entrainment, as compared with gas entrainment due to vortex formation. Presented is a preliminary experimental investigation to demonstrate quantitative measurements of the liquid flow field at the onset of gas entrainment in a single discharging bottom branch. The three dimensional flow field is resolved into three horizontal planes and a single vertical plane. Results indicate a strong dependency of the flow field on the radial component, directed toward the branch center, and where a solid wall is present a larger tangential component.