This document describes a new efficient method for sampling atmospheric methane for radiocarbon analysis. The method separates methane from air directly at the sampling site, minimizing handling and speeding up the analysis process. Test runs of the new sampler achieved high-precision radiocarbon measurements of methane. Initial results from samples in London suggest fossil fuel methane contributions to emissions are greater than estimated by inventories, possibly due to underestimation of gas leaks. Further background and modeled measurements are planned to improve source partitioning of methane emissions.