[en] We have been exploring the development of multicomponent gas mixtures with optimal electron transport, gain, electrical and chemical properties of potential interest to the Superconducting Super Collider muon detectors focusing in particular on binary and ternary mixtures of Ar, N₂, CO, CO₂, CH₄, CF₄, NH₃, and H₂O. In this article, we report and discuss: (i) recent measurements of electron drift velocities as a function of the density-reduced electric field E/N for CO₂/CF₄, CO₂/CH₄, CO₂/N₂, CO/Ar, Ar/Si(CH₃)₄, NH₃/CF₄/Ar, CO₂/CF₄/Ar, and H₂O/CF₄/Ar mixtures, (ii) calculated values of the mean electron energy as a function of E/N for a number of unitary gases and the gas mixtures CO₂/CF₄, CO₂/CH₄, and CF₄/Ar, and (iii) effective ionization coefficients as a function of E/N for Ar/CF₄, Ar/CO₂, CO₂/CH₄, and mixtures of Ar/CF₄ containing CO₂ or H₂O. Addition of CO₂ or H₂O or NH₃ to CF₄/Ar causes electron 'cooling' and increases the electron yield; the addition of H₂O (or NH₃) may, also, improve the detector aging performance. Mixtures of Ar/CF₄ with CO₂ or H₂O appear promising. All results reported are for the case of zero magnetic field. (orig.)