Volcanic systems are challenging environments in which to accurately sample or measure gaseous mercury (Hg) concentrations, as the gas plumes may be hot, acidic and halogen-rich; Hg concentrations may be highly variable; and the environment may not be readily accessible. We conducted an inter-method comparison study of atmospheric Hg measurements at Icelandic volcanic systems using four different methods. These included a passive air sampler (PAS), an active sampler with activated carbon trap (ACT) and two real-time measurement instruments, the Lumex portable mercury analyzer and the Tekran automated mercury analyzer. Good agreement in calculated and time-averaged volcanic plume Hg concentrations (ranging from 2.3 to 7.2 ng m−3) was obtained between the ACT and Lumex methods operated simultaneously at the same sites. In a post-fieldwork intercomparison, ACT and Tekran sampling yielded excellent agreement in measuring background atmospheric Hg concentrations. However, PAS-measured concentrations were significantly lower than the other methods, and in many cases were below the method detection limit, which may be due to the short sampling timeframes and/or adverse meteorological conditions not allowing sufficient Hg to be collected on the samplers. These findings demonstrate that Lumex and ACT methods are suitable for gaseous Hg measurement in volcanic gas plumes. •We compared four gaseous mercury measurement methods at volcanic sites.•Activated carbon trap sampling agreed well with Lumex and Tekran results.•Passive samplers yielded significantly lower mercury than other methods.•Further tests are needed to assess passive samplers in sulfur-rich volcanic gases.