Neutron–nuclear interaction cross-section is sensitive to neutron kinetic energy and most nuclei exhibit resonance behaviour at specific energies within the resonance energy range, spanning from a fraction of an electron volt to several tens or hundreds of kilo electron volts. The energy positions of these resonances correspond to the excitation energy levels of the compound nucleus that are formed as intermediate states during the interaction. Though these positions, thanks to sophistication in science and technology, are known reasonably precisely for the materials of reactor interest, deviations or spread in this data among different evaluations cannot be ruled out. In this work, the effect of such a spread in the resonance positions of the reactor materials on the multiplication factor of an infinite reactor, is obtained. The study shows that the effect on a thermal reactor is more pronounced than on a fast reactor.