A previously described experimental method of determining initial conversion ratios in reactor lattices has been improved. Measurements have been made on D2O-cooled, 19-element UO2, heavy-water lattices at pitches of 18, 21, 24, 28, and 36 cm. The initial conversion ratios obtained were 0.9547 ± 0.0086, 0.8578 ± 0.077, 0.7671 ± 0.0069, 0.7416 ± 0.0067, and 0.6853 ± 0.0062 and the resonance escape probabilities derived are 0.8226, 0.8656, 0.9104, 0.9228, and 0.9511, respectively. The fast fission factors obtained for the 18, 24, 28, and 36 cm lattice pitches were 1.0283, 1.0265, 1.0253, and 1.0247.