Vibrational quenching rate coefficients k(q) have been measured from thermal energy to 0.3 eV mean relative kinetic energy KE(cm) for NO+(v = 1 or 4) and O-2(+) (v = 1 or 2) ions in collisions with He by using a monitor ion technique in a selected ion flow drift tube. All these values for k(q) increase dramatically with increasing KE(cm). These quenching processes have also been investigated theoretically by using simple collinear models which yield rate coefficients in good agreement with the measured values.