The rates and products of the purely heterogeneous oxidations of C2H6(g) and C2H4(g) on Sm2O3 in the presence of O-2(g) were investigated in a very low-pressure flow reactor by on-line molecular beam mass spectrometry, about 1000 +/- 100 K. Ethane is oxidized to ethyl radicals, which undergo unimolecular decomposition into (C2H4 + H) or further oxidation to CO. C2H4 oxidation leads to CO as initial product, that is subsequently converted into CO2. Steady state rates are proportional to k(i)’([O-2]) x [C2Hn], with k(i)’([O-2]) = k(i) x (K-i[O-2])(1/2)-/{1+(K-i[O-2])(1/2)} (i = 3, 4 for n = 6, 4, respectively), which is consistent with the direct oxidation of hydrocarbons on surface oxygen species in dissociative equilibrium with O-2(g). Alternate or simultaneous measurement of the oxidation rates for C2H6, C2H4, and CH4, the latter proportional to k(1)’[CH4], on the same Sm2O3 sample as function of [O-2] and temperature, led to the following expressions : log (k(3)/k(1)) = -(0.14 +/- 0.30) + (663 +/- 300)/T (I), log(k(1)k(1)) = (1.08 +/- 0.35) - (645 +/- 365)/T (II), log (K-1/nM(-1)) = (2.76 +/- 0.46) - (4363 +/- 458)/T (III), log (K-3/nM(-1)) = (1.85 +/- 0.22) - (4123 +/- 260)/T (IV), log(K-4/nM(-1)) (5.31 +/- 0.65) - (6480 +/- 647)/T (V) (nM 10(-9)M), that are independent of catalyst mass, active area, or morphology. Equations I-V imply that ethane and ethylene are oxidized faster than methane at all relevant temperatures, Although the activation energies, E(4) > E(1) > E(3), correlate with the corresponding BDE(C-H) energies suggesting a common H-atom abstraction mechanism, the A-factor for the oxidation of ethylene is about tenfold larger. Oxidations occur on distinguishable O-6 species generated by endothermic, exentropic O-2 chemisorption involving cooperative participation of the solid.