All of the published experimental values of longitudinal and transverse diffusion coefficients of gaseous ions in electric fields, except those cases dominated by resonant charge transfer, are compared with the predictions of Wannier's theory. The products of the measured coefficients and the gas number density appear to vary as $v_d^{{}^3}{\left(\frac{E}{N}\right)}^{-1\mathrm{}}$, where $v_d$ is the ionic drift velocity, in agreement with Wannier's predictions. Here $\frac{E}{N}$ is the ratio of the electric drift field intensity to the gas number density. In addition, the absolute agreement between experiment and theory is quite satisfactory.

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