Critical parameters are reported for an essentially unreflected system containing uranium solution and a fixed neutron poison. The uranium solution contained 450.8 g of uranium per liter. The uranium was enriched to 93.19 wt% 235U. The fixed poison was natural boron contained in stainless steel plates and comprised 1.02 wt% of the plates. The total boron content was varied on successive runs by changing the number of plates. The plates were arranged along parallel chords of the 106.6-cm-diam cylindrical experimental tank; they were approximately uniformly spaced. Three types of measurements are reported. The first type provides data on an unpoisoned slab. In the second type, the uranium solution height at criticality was less than the height of the plates (119 cm) and provided data on a poisoned solution cylinder. When the boron concentration was 16.41 g/liter, the cylinder was sub-critical even if infinitely long. The third type of measurement, where the critical uranium solution height exceeded the plate height, allowed an evaluation of the interaction between an unpoisoned slab and a highly poisoned region. The highest boron concentration measured was 20.62 g/liter. The experimental data are compared with results from neutron transport and diffusion computer codes. Computer results also provide asymptotic values for critical parameters not amenable to measurement because of apparatus limitations. Finally, the computer was used to extend the applicability of the data to more general systems.