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The global search for natural hydrogen has sparked a re-evaluation of all vintages of data in numerous geological regions. Legacy well data from Denmark indicate a potential occurrence of H 2 , which highlights the need for a full evaluation of data from the onshore Danish area. Based on a systematic review of 85 legacy well reports from the onshore parts of the Norwegian–Danish Basin and the Danish part of the North German Basin, we show that H 2 , He and N 2 are widespread across the Danish onshore region. Modern H 2 data are consistently low across onshore Denmark and fail to reproduce the elevated values recorded in the Tønder wells, located in the North German Basin, which were drilled during early oil and gas exploration activities in the 1950s. He concentrations vary from low to moderate, suggesting a possible commercial potential in parts of the onshore Danish region. The poor understanding of the deepest parts of the onshore Danish region, where potential sources for H 2 and He may be present, combined with the highly varying methods for sampling and analyses used for the reported H 2 and He occurrences, constitute the main limitations for a deeper understanding of the subsurface fluid–gas system in the area. However, the Danish onshore region potentially encompasses several H 2 and He sources, which are associated with organic-rich, overmature radiogenic shales and granitoid basement. No areas with extensive serpentinization have been recognized.