Addition of nonelectronegative molecules (n-alkanes, alkenes, CO, CO2) to liquid argon, krypton, and xenon influences the drift velocity of excess electrons in an electric field. At high field strengths (104–105 V cm−1), where the electrons have mean energies exceeding kT, inelastic collisions with solute molecules lead to an increase of the drift velocity above the value of the pure solvent. Analysis of this effect yields the energy dependent product of collision cross section and mean fractional energy loss per collision.At low field strengths a decrease of the low field mobility with increasing solute concentration is observed from which the cross section for momentum transfer could be deduced. The influence of solutes on the low field mobility was also found in tetramethylsilane.