A model is presented for the split of annular gas/liquid flow at a horizontal T-junction. It employs a sub-model which assumes a specific fraction of liquid to be entrained as drops, and utilizes film thickness/shear stress relationships and particular forms of velocity profiles within the film to determine the circumferential variation of film flow rate. The model can successfully predict the phase split for large diameter (0.127 m) junctions as well as those with smaller diameters. It is suggested that poorer predictions might be caused by incorrect values of entrained fraction being used. The results of the horizontal annular flow sub-model are used to examine the assumptions of the split model.