[en] The electron drift velocity, the longitudinal diffusion coefficient and the effective ionization coefficients in C₂F₆ and its mixtures with Ar and N₂ have been studied in a pulsed Townsend experiment. The density-reduced electric field strength E/N, was varied widely in the range 0.1-500 Td (1 Td = 10^-17 V cm²). In all cases, negative differential conductivity (NDC) regions were found in the plots of the electron drift velocity as a function of E/N. Our drift velocity values were found to be in good agreement with previous work on C₂F₆ and its mixtures. In some cases, the E/N range was increased. The longitudinal diffusion coefficient also displays the NDC effects; these are more pronounced as the C₂F₆ content in the mixture decreases. The effective ionization coefficient for C₂F₆ was measured over a wider range of E/N than that covered by previous studies. Our effective ionization coefficients for C₂F₆ and those derived previously disagree strongly. We are not aware of any previously published data on effective ionization coefficients for the mixtures herein studied. The limiting field strength for C₂F₆-N₂ turned out to be nearly a factor of two higher than that for C₂F₆-Ar, for C₂F₆ concentrations being less than 10% in both mixtures