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Baseline surveys provide essential information to ascertain the "a priori" conditions beforemajor exploration (or other works) which could result in a significant release of methane tothe atmosphere. However, it is not often as easy as simply measuring the methane mixingratios downwind of a prospective site as many sources of methane may be contributingto the local atmospheric mix. We need to find a way of being able to definitivelyco-locate elevated methane to sources during the baseline survey so that any postexploration increases can be correctly attributed. Multiple campaigns have beenundertaken around the UK and Australia in order to ascertain baseline atmosphericmethane prior to and in the early stages of unconventional gas exploration andproduction. Work in Northern England has focused on two sites, near to Blackpool which hassubsequently become an active shale gas fracking site, and the Vale of Pickering which is stillat the site preparation stage. The Australian component is centred on the Surat Basin,Queensland. All three sites pose an interesting mix of methane sources, with influencesranging from agriculture, coal mines, landfill and gas infrastructure leaks. Here, wedemonstrate the value in using mobile surveys along with ethane:methane ratios, δ13CCH4 orboth to allow source identification, and also consider whether the addition of δDCH4 is alsonecessary in certain circumstances. Complexity is increased where there are overlappingplumes. For baseline surveys to be useful in determining the impact of later emissions, theymust be able to differentiate between both surveyed sources and the potential futuresources of methane, as well as being thorough enough to identify current fugitiveemissions. Variability of meteorological conditions can cause significant changesto where emissions can be sampled and we investigate whether a single surveycan accurately capture all the major influencing sources of methane for a region? [ABSTRACT FROM AUTHOR]