The reported dataset is annexed to the article “Intense overpressurization at basaltic open-conduit volcanoes as inferred by geochemical signals: the case of the Mt Etna December 2018 eruption”. It consists of five types of parameters: soil CO₂ flux from Mt Etna flanks, CO₂/SO₂ molar ratio of the volcano plume, SO₂ and HCl fluxes by volcano plume, and He isotope ratio in some peripheral gas emissions, all of them recorded in the period 2017–2019. The data come from continuous monitoring networks installed on Mt Etna and from discrete samplings carried out at specific sites, all the monitoring facilities being supported by the INGV-Civil Defence joint surveillance program.