An approach to reactor physics is developed by analysis of experimental data on ordinary water, slightly enriched uranium lattices. The developed procedure is extremely simple, and for these particular lattices, it is demonstrated that the thermal utilization factor and resonance escape probability can be calculated to satisfactory accuracy. Generalization of the procedure to all types of lattices is discussed, and a number of graphite moderated lattices are analyzed. However, detailed analysis of further experimental data is required before the generalization can be used with complete confidence. To illustrate the reasonableness of the proposed general approach and hence the desirability for continued investigation along these lines, results of criticality and core-life calculations are presented for the Calder Hall reactor and for the Yankee reactor with various enrichments.