Understanding gas transport processes in clay barriers is crucial for assessing the long-term safety of geological repositories for radioactive waste. Fundamental and well-designed experimental research at the laboratory scale is an indispensable prerequisite for conceptualising gas transport mechanisms and their simulation at repository scales. In practice, however, it turns out that comparing gas invasion experiments on argillaceous rock samples is difficult since different laboratories use different test protocols. This paper presents a collaborative and comparative study conducted by two teams from the Geotechnical Laboratory at the Universitat Polit & egrave;cnica de Catalunya (UPC, Spain) and the Laboratory of Soil Mechanics at the Swiss Federal Institute of Technology of Lausanne (LMS/EPFL, Switzerland), carried out as part of the European Joint Programme EURAD. Both teams employed equivalent gas testing protocols to characterise two argillaceous host rocks: Boom Clay (Belgium) and Opalinus Clay (Switzerland). The integrated workflow enabled the determination of common features regarding the hydro-mechanical response of the tested samples. This research underscores the importance of verifiable testing methods to enhance the understanding of gas transport in geological repositories. The results highlight the benefits of coordinated efforts and shared methodologies in advancing geotechnical research and fostering collaboration among national agencies.