As most part of the industrial effluents contain carbon dioxide and water vapour, it is interesting to study from an electric point of view ‘basic’ gas mixtures including air and various amounts of these gases, in order to precise how the corona discharge inception takes place in such mixtures. In a DC point-to-plane reactor, distinct parameters are varied, such as discharge current, partial pressure of CO2, and relative humidity. Gap voltage and streamer frequency are experimentally measured as functions of the discharge current. Current waveforms are recorded in various gas mixtures and electrical conditions. DC and impulsional current components, as well as streamer frequency are also plotted as functions of the CO2 partial pressure for dry and water saturated mixtures. For dry or wet mixtures, 5% CO2 in volume appears to be the proportion allowing the establishment of a stable corona discharge with the lowest energy cost.