Values of the ionization (&agr;/N) and attachment (&eegr;/N) coefficients have been determined from spatial current growth measurements in uniform fieldsEfor a CO2 : N2 : He (1 : 2 : 3) mixture and for pure CO2over the ranges 4.66×10−16⩽E/N⩽8.48×10−16V cm2and 7.63×10−16⩽E/N⩽9.89×10−16V cm2, respectively, whereNis the gas density. The limiting values ofE/N, at which &agr;=&eegr;, are found to be (4.66±0.14) ×10−16V cm2and (8.20±0.16) ×10−16V cm2for the CO2 : N2 : He mixture and for CO2, respectively. The present values of the coefficients are in reasonably good agreement with those calculated from a solution of the Boltzmann equation using electron‐collision cross sections. Nevertheless, the present results indicate that even closer agreement would be obtained if the attachment cross section used in the calculations is reduced by about 15&percent;.