Security of gas supply is a crucial stake for the European countries. The ProGasNet simulator has been developed by the European Commission to study the vulnerability of the gas network to different threats. With the simulator the European gas network (or a portion of the network) can be modelled. But several uncertainties are present in the models. Therefore, it is important to analyse the impact of these uncertainties on the model-based inferences. This report presents an uncertainty and sensitivity exercise of the security of gas supply model of an anonymised EU gas transmission network of several members. The uncertainty analysis shows that, for some scenarios of gas supply disruption, due to the uncertainties in the input parameters it cannot be clearly concluded whether the network is reliable (i.e. can supply the demand of the countries) or not. The sensitivity analysis points out the uncertain inputs mostly responsible for this lack of precision. It is found that priority should be given to the better assessment of the peak demand of the studied countries if one wants to get reliable results. Additionally, the study also highlights areas where the studied infrastructure can be improved.