Due to uncertainties that are inevitably involved in our understanding of the system and its behaviour, discussions on issues relating to long-term effectiveness of geological storage of CO2 should not be closed within the scientific community. Rather a variety of stakeholders who have distinct interests and value systems need to be involved. On the other hand a spectrum of evidence supporting long-term confinement of CO2 in a reservoir with favourable characteristics is available. In this study a comprehensive methodology that can deal with different perspectives of stakeholders and make use of various pieces of evidence in a mutually complementary manner by using argumentation models is developed and applied to a series of exercise.