A field sampling campaign spanning the entire western margin of the Greenland Ice Sheet was conducted in the summer melt seasons of 2021, 2022, and 2023, to measure release of dissolved methane from meltwater streams draining the subglacial environment of the Greenland Ice Sheet. The campaign was designed to assess whether subglacial methane export is ubitiqous from the GrIS, and the source and age of this methane released.Twenty-six rivers draining from the GrIS were sampled in the summers of 2021, 2022 and 2023 along the west coast of Greenland, forming a north to south transect from Qaanaaq to Narsarsuaq. We split these rivers into regional areas of northwest (NW), central west (CW), and southwest (SW). Most of these rivers drained directly from the subglacial environment, whether via an upwelling (proglacial spring) or subglacial portal. Samples were taken as close to the upwelling or portal as possible, to get the most representative view of the subglacial system, with limited off-gassing or dilution effects from supraglacial meltwaters. Basic stream geochemistry (pH, EC, O2) was measured in the field using a WTW 3430 multimeter. Dissolved CH4 was extracted (Garnett et al., 2016) into a nitrogen headspace, via 5L water samples were collected into a 10L accordion water carrier, 1-2L of pure N2 headspace was added and the water carrier was shaken for 3 minutes to equilibrate the CH4. The headspace CH4 concentrations were measured directly in the field using a using a micro portable greenhouse gas analyser (MGGA, ABB GLA1313 Series, using Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) technology). The headspace with extracted sample was stored in a pre-evacuated 15L Silonite™ cannisters with TrueSeal Valve™ (Entech Instruments) or pre-evacuated 150ml glass serum vials (Wheaton™) using a 150 ml glass syringe and sealed with 15 mm crimped (13mm) chlorobutyl rubber stoppers (Bellco Glass) ahead of radio- and stable- carbon isotope analysis, respectively. We provide measured and 'corrected' radiocarbon ages of dissolved methane. We recognise that the CH4 extracted and measured in each water sample is a homogenised sample, likely containing subglacially produced CH4 combined with some modern CH4, when supraglacial water is routed through moulins to the bed and through the subglacial system. Therefore, it is likely that our water samples encompass some portion of modern-day CH4, and accounting for this provides a more accurate assessment of the 14C-age of the subglacial carbon source for methanogenesis. We used a simple mass balance approach to consider what proportion of our sampled CH4 is potentially modern-day atmospheric, based on the measured atmospheric CH4 concentration measured during a survey of the supraglacial area inland.