Exponential and approach-to-critical experiments have been conducted with slightly enriched uranium in light water. The uranium was fabricated into elements of 0.175 to 1.66 in. diam with enrichments of 1.007 to 3.063 wt% U235. Exponential measurements have also been made with natural uranium rods (0.925 in. diam) in light water. Analytical methods were used to correlate the experimental results and extend the data to include uranium rods containing 4.0 and 5.0 wt% U235.