The oxidation reactions of all of the lanthanide cations (except Pm+) with N2O and O-2 have been investigated using the inductively coupled plasma selected-ion flow tube (ICP/SIFT) technique. Lanthanide cations were generated in an inductively coupled plasma (ICP) ion source. Observations are reported for the reactions of La+, Ce+, Pr+, Nd+, Sm+, Eu+, Gd+, Tb+, Dy+, Ho+, Er+, Tm+, Yb+, and Lu+ with N2O and O-2 at room temperature (295 +/- 2 K) in helium at a total pressure of 0.35 +/- 0.02 Torr. Measured reaction rates varied from close to the predicted ion-molecule collision rate down to less than 0.1% efficiency. Observations are rationalized in terms of reaction thermodynamics and electronic structure effects. The efficiency for the reactions with N2O was found to decrease as the energy required to promote the metal-ion electron from the 4f(n)5d(0)6s(1) to the 4f(n-1)5d(1)6s(1) configuration increases. Remarkable and different Arrhenius-like correlations are found in the N2O reactivity of the early and late lanthanide cations with this electron promotion energy.