Bagana is a remote, highly active volcano, located on Bougainville Island in southeastern Papua New Guinea. The volcano has exhibited sustained and prodigious sulfur dioxide gas emissions in recent decades, accompanied by frequent episodes of lava extrusion. The remote location of Bagana and its persistent activity have made it a valuable case study for satellite observations of active volcanism. This remoteness has also left many features of Bagana relatively unexplored. Here, we present the first measurements of volcanic gas composition, achieved by unoccupied aerial system (UAS) flights through the volcano’s summit plume, and a payload comprising a miniaturised MultiGAS. We combine our measurements of molar CO₂/SO₂ ratio in the plume with coincident remote sensing measurements (ground- and satellite-based) of SO₂ emission rate, to compute the first estimate of CO₂ flux at Bagana. We report low SO₂ and CO₂ fluxes at Bagana from our fieldwork in September 2019, ~320 ± 76 td^-1 and ~320 ± 84 td^-1 respectively, which we attribute to the volcano’s low level of activity at the time of our visit. We use satellite observations to demonstrate that Bagana’s activity and emissions behaviour are highly variable and advance the argument that such variability is likely an inherent feature of many volcanoes worldwide and as yet is inadequately captured by our extant volcanic gas inventories, which are often biased to sporadic measurements. We argue that there is great value in the use of UAS combined with MultiGAS-type instruments for remote monitoring of gas emissions from other inaccessible volcanoes.