The electron swarm characteristics in gas mixtures containing CF_4 has been analysed over the E/N range 0.01-566Td by a multi-term Boltzmann equation method and by a Monte Carlo simulation. The differences between CF_4 and Ar, and CF_4 and N_2 mixtures, in electron transport coefficients have been explained by the calculated electron energy distributions and the respective sets of electron collision cross-sections. The synergistic behaviour and the dielectric characteristics in these gas mixtures have been also shown and discussed in detail.