We have measured and report the total gas‐number‐density normalized effective ionization coefficient, &agr;¯/N, as a function of the density‐reduced electric field,E/Nfor Ar, CO2, CF4, the binary gas mixtures CF4:Ar (20:80), CO2:Ar(20:80), CO2:CH4(20:80) and for the ternary gas mixtures CO2:CF4:Ar (10:10:80) and H2O:CF4:Ar(2:18:80). We also report the limiting value, (E/N)limof the above gaseous systems. A comparison of our results on the unitary gases shows good agreement with previous measurements. The results on the ternary mixtures show that the addition of CO2or H2O to the binary gas mixture CF4:Ar lowers the electron energies and increases &agr;¯/N(E/N).