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Methane emission fluxes from facility-scale sources may be poorly quantified, leading to uncertainties in the global methane budget. Accurate atmospheric measurement based flux quantification is urgently required to address this. This paper describes the test of a new near-field Gaussian plume inversion (NGI) technique, suitable for facility-scale flux quantification, using a controlled release of methane gas. Two unmanned aerial vehicle (UAV) platforms were used to perform 22 flight surveys downwind of a point-source release of methane gas from a regulated and flow-metered cylinder. One UAV was tethered to an instrument on the ground, while the other UAV carried an on-board high-precision prototype instrument, both of which used the same near-infrared laser technology. The performance of these instruments from UAV sampling is described. Both instruments were calibrated using certified standards, to account for variability in the instrumental gain factor. Furthermore, a modified approach to correcting for the effect of water vapour applied and is described here in detail. The NGI technique was used to derive emission fluxes for each UAV flight survey. We found good agreement of most NGI fluxes with the known controlled emission flux, within uncertainty, verifying the flux quantification methodology. The lower NGI flux uncertainty bound was, on average, 17 % ± 10(1σ) % of the controlled emission flux and the upper NGI flux uncertainty bound was, on average, 218 % ± 100(1σ) % of the controlled emission flux. These highly conservative uncertainty ranges incorporate factors including the variability in the position of the plume and the potential for under-sampling. While these average uncertainties are large compared to methods such as tracer dispersion, we suggest that UAV sampling can be highly complementary to a toolkit of flux approaches and may perform well in situations where site access for tracer release is problematic. We see tracer release applied to UAV sampling as an effective combination in future flux quantification studies. Successful flux quantification using this UAV sampling methodology demonstrates its future utility in identifying and quantifying emissions from methane sources such as oil and gas infrastructure facilities, livestock agriculture and landfill sites, where site access may be difficult. [ABSTRACT FROM AUTHOR]