The transformation of vinyloxirane and ethyloxirane were studied on Pt-SiO2 and Pd-SiO2 catalysts at 273 and 301 K in a recirculation reactor, in the presence of hydrogen or deuterium. There are significant differences, not only in reaction rates, but also in reaction routes, depending upon the nature of the metal. The main reaction routes are : deoxygenation and hydrogen or deuterium addition on Pt-SiO2; isomerization and hydrogenolysis on Pd-SiO2, The reaction routes leading to the formation of the individual products are interpreted on the basis of the experimental results. In the case of the hydrogenolysis of oxiranes, Pd was shown to exhibit a special reactivity, unlike earlier observations described in the literature.