Using air and water as the working fluids, phase separation phenomena for stratified and plug flows at inlet were investigated experimentally, at a simple T-junction and specifically designed multitube T-junction separators with two or three layers. The results show that for these two flow patterns the separation efficiency of the two phases for any multitube T-junction separator is much higher than that of the simple T-junction. Increasing the number of connecting tubes in the multitube T-junction separator can increase the separation efficiency. Generally, for stratified flow, complete separation of the two phases can be achieved by the two-layer multitube T-junction separator with five or more connecting tubes and by the three-layer separator; increasing the gas flow rate, the liquid flow rate, or the mixture velocity under plug flow is detrimental to phase separation with a drop in peak separation efficiency. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 2285-2292, 2017