We report results from a worldwide inter-laboratory comparison of samples among laboratories that measure (or measured in the past) stable carbon and hydrogen isotope ratios of atmospheric CH4 (δ13C-CH4 and δD-CH4). The offsets among the laboratories are larger than the measurement reproducibility of individual laboratories. To disentangle plausible measurement offsets, we evaluated and critically assessed a large number of intercomparison results, some of which have been documented previously in the literature. The results indicate significant offsets of δ13C-CH4 and δD-CH4 measurements among datasets reported from different laboratories; the differences among laboratories at modern atmospheric CH4 level spread over ranges of 0.5‰ for δ13C-CH4 and 13‰ for δD-CH4. The intercomparison results summarized in this study may be of help for future attempts to harmonize δ13C-CH4 and δD-CH4 datasets from different laboratories in order to jointly incorporate them into modelling studies. However, establishing such a merged dataset, which includes δ13C-CH4 and δD-CH4 data from multiple laboratories with desirable compatibility, is still challenging due to differences among laboratories in instrument settings, correction methods, traceability to reference materials and long-term data management. Further efforts are needed to identify causes of the inter- laboratory measurement offsets and to decrease those towards the best use of available δ13C-CH4 and δD-CH4 datasets.