The hydrogenative ring-opening reactions of methyl- and propylcyclobutane were studied over Ni/SiO2 catalyst in wide temperature and hydrogen pressure ranges. Firstly, the temperature dependence of ring opening was determined and maximum curves were observed for both reactants. On the basis of the temperature dependence curves, various temperatures were selected for hydrogen pressure studies. At both 523 and 573 K, only hydrogenative ring opening occurred, and the ring opened mostly in the sterically less hindered direction in the case of methylcyclobutane over clean as well as working catalysts. However, for propylcyclobutane the selectivity was close to statistical or opposite to that for methylcyclobutane, especially at lower hydrogen pressures over the initial catalyst. At the lowest temperature at which ring opening occurred at all, exclusive heptane formation (ring opening in the more hindered direction) was observed. The hydrogen pressure dependence curves over the initial and working catalysts were used to draw mechanistic inferences concerning the ring-opening reactions.