To investigate the impact of solid (confinement) wall on a perturbed liquid sheet co-moving with two moving gas streams, a linear instability analysis was conducted. The analysis focussed on a fundamental varicose mode of initial disturbance and was carried out at varying Reynolds numbers (Re = 100 and 1000) and gas–liquid velocity ratios. The findings suggest that confinement destabilized the perturbed liquids sheet, with the destabilizing effects being more pronounced at lower gas–liquid velocity ratios. As the confinement height increases, the confinement’s impact starts to diminish, and there is no significant change in the linear growth rate higher than a certain value. Additionally, the largest confinement height (Chmax) decreases as U increases, with Chmax becoming invariant beyond a critical value ( \({\mathop{U}\limits^{\frown}}\)  = 7 for Re = 100 and = 5 for Re = 1000). Moreover, Chmax decreases with an increase in Reynolds number, indicating that liquid viscosity enhances the impact of confinement.