Reactor physics parameters were measured in three heavy water lattices consisting of 0.250-in.-diam, 1.03 wt% 235U metal fuel rods in triangular arrays spaced at 1.25, 1.75, and 2.50 in. The following quantities were measured in each lattice: the ratio of epicadmium to subcadmium radiative captures in 238U (ρ28); the ratio of epicadmium to subcadmium fissions in 235U (δ25); the ratio of radiative captures in 238U to fissions in 235U (C); and the fissions in 238U to fissions in 235U (δ28). These experimental results were used to calculate the following reactor physics parameters for each lattice: the resonance escape probability p, the fast fission factor ϵ, the multiplication factor for an infinite system k∞, and the initial conversion ratio C. Analytical results obtained by using THERMOS and GAM-I are in fair agreement with the experimental results.