In the present investigation, a Four-Stream Model was derived for predicting the phase-distribution of two-phase stratified flow at horizontal T-junctions. The present model was based on integrating the energy equation over four control volumes: gas inlet-to-run, gas inlet-to-branch, liquid inlet-to-run, and liquid inlet-to-branch. These four energy equations were combined algebraically to obtain a single equation which predicts the mass fraction of liquid that exits through the branch tube given the mass fraction of gas that exits the branch tube. Several simplifying assumptions were made to obtain the final model equation. A single-phase format was used for the gas and liquid energy equation imbalance terms, with the addition of two-phase multipliers to account for the differences between single-phase flow and two-phase flow. The phase-distribution database was compiled from experimental flow-split data from several sources. These data combined form a substantial amount of stratified- and wavy-flow data at diameter ratios of 1. and 0.5. The predictions of the present model were studied at several sets of inlet conditions. (Abstract shortened by UMI.)