A series of subcritical multiplication experiments was conducted at Purnima Laboratories, Trombay, on a thick BeO-reflected 233U (98.2 wt% enrichment) uranyl nitrate solution system. The core tank was a rectangular parallelepiped of 0.11− × 0.11−m2 sectional area attached to the bottom of a glove box. Multiplication measurements were carried out with uranyl nitrate solutions in the uranium concentration range of 25 to 150 kg/m3 corresponding to H/233U ratios in the range of 1200 to 200. The maximum quantity of 233U-enriched uranium used was 0.12 kg and the corresponding multiplication was ∼5. Boric acid solutions, equivalent in terms of thermal-neutron absorption to the uranium solutions, were used to eliminate the unmultiplied neutron background and to calibrate the neutron detection system. Extrapolated critical heights determined from plots of inverse multiplication were used to obtain the keff of the subcritical assembly with the help of the Trombay Criticality Formula. Absolute multiplication and keff were also deduced independently from the observed multiplication data relative to a reference dummy core. The experimental keff results are found to be in good agreement with detailed transport theory and Monte Carlo calculations.