ABSTRACT The motion of a long gas bubble in a continuous liquid phase in a small diameter channel results in a thin liquid film between the bubble and the channel wall. Generally, a free-slip (zero shear) boundary condition is applied at the gas–liquid interphase boundary which is applicable only at low gas velocities. However, at increased flow rates of gas phase, shear stress at the gas–liquid interface is non-negligible. Applying non-zero shear at the interface requires knowledge of velocity profile in the gas phase. In this work, we circumvent this problem by using a slip length like parameter to take into account the velocity gradient in the gas phase. The slip length is infinite for the free-slip condition at the interface and zero for the no-slip condition. An expression is derived for the film thickness in terms of slip length and capillary number and is compared with the experimental data and other correlations available in the literature.