<p>This paper presents a novel investigation into the physics behind the multiple liquid level solutions in upward gas–liquid stratified flow, addressing a longstanding challenge in two-phase flow analysis. Using a simplified approach, we apply the combined momentum equation (CME) to uncover the physical basis for identifying the correct root from the multiple possible solutions. Each term in the CME distinctly impacts the selection of these roots, providing new insight on this phenomenon. Our findings reveal that the multiple-root solution arises near the transition to conditions where localized backflow occurs at the wall, while the overall flow remains forward. Among the solutions, the smallest liquid level consistently represents the physically accurate outcome. This behavior is further supported by experimental data from established literature. Additionally, the stable root is shown to reside near the region of minimum total energy—where the kinetic energies of both the liquid and gas phases converge. This research not only validates these findings experimentally but also delivers fresh insights into the energetic characteristics of stratified two-phase flow, offering a new methodology not previously explored in the literature.</p>