Analytical and experimental laboratory studies were conducted for rapid pressurizing of entrapped gas at the end of a horizontal liquid pipeline. In this paper analytical and experimental model study are presented for pressurizing entrapped gas pocket at the end of a liquid column in a horizontal pipeline. Analytical models are considered such as (1) acoustic effect of both liquid and gas side, (2) variation of liquid length, and (3) thermal damping process. Closed form of solutions were derived for a lumped liquid and lumped gas model if pipeline is a horizontal. Experiments were conducted to verify the analytical models. Comparison of analytical and experimental model results were presented. Analytical model was developed to define the physics behind the gas venting case. Experiments were conducted for a range of orifice sizes from 1/16 to of the pipe diameter with reservoir pressure two, three and four times of ambient pressure for five different pipe configurations. Experimental results confirm the assumption of modified entrapped air model is correct.