Cryogenic propellant tanks are sufficiently pressurized with cryogenic vapor or inert gas to maintain and control the flow rate of the fuel at any time of the mission. Condensation in the ullage of the propellant tank during and after pressurization can cause pressure loss in the tank which is augmented by wave motion interface induced by engine thrust or stage separation or any other external forces. Present study focusses on understanding the effects of the inlet conditions of the pressurant gas on the pressure evolution and thermal stratification in the tank and the pressurant mass requirement at different liquid levels during pressurization. Experiments are conducted in laboratory scale using LN2 as working fluid and GN2 as pressurant gas to understand the phenomena. A parametric study has been carried out to study the effect of ullage volume and pressurant gas (GN2) flow rate (0.25-2 g/s) and temperature (250-350 K) on the pressure evolution and thermal stratification in the tank after appropriate validation. Numerical simulations revealed that mass condensed during the pressurization is a weak function of ullage depth and temperature but a strong function of the mass flow rate. The pressurant gas temperature has a strong influence on the flow pattern in the ullage. The pressurant gas flows along the wall and reaches the interface without disturbing the bulk vapor. Heat transfer at the interface is dominated by the heat carried by the pressurant than by transfer from the bulk vapor.