The development of reliable hydrogen sensors is crucial for the safe use of hydrogen. One of the main concerns of end-users is sensor reliability in the presence of species other than the target gas, which can lead to false alarms or undetected harmful situations. In order to assess the selectivity of commercial of the shelf (COTS) hydrogen sensors a number of sensors of different technology types were exposed to various interferent gas species. Cross-sensitivity tests were performed in accordance to the recommendations of ISO 26142:2010, using the hydrogen sensor testing facilities of NREL and JRC-IET. The results and conclusions arising from this study are presented.