An engineering physics method of calculation has been used to plan and interpret critical experiments that simulate a boiling reactor and a boiling reactor with integral nuclear superheat. The boiler region contains aluminum-clad fuel rods of 1.85 wt.% U235 enrichment and some rods of natural enrichment. The superheater region is composed of rod-in-tube elements, the fuel rod having 3.41 wt.% U235 enrichment and a stainless steel clad. For core arrangements containing boiler fuel, the variations in reactivity and rod-by-rod power distributions produced by changing fuel, moderator, and neutron poison content within a fuel assembly have been determined; also, reactivity measurements involving cadmium and boron-stainless steel control rods have been used to derive effective epithermal transmission probabilities for these materials. For the boiler-superheater cores, the variations in reactivity, power regulation, and rod-by-rod power distribution produced by changing the boiler-superheater arrangements, and by voiding and flooding the superheater region, have been determined. For most of the core arrangements, the theoretical predictions have been carried out prior to the measurements. The comparison of theory with experiment indicates that the method has calculated reactivity and rod-by-rod power distributions to within the limits imposed by the uncertainty of experimental techniques, which includes uncertainties in core dimensions and compositions.