The critical thickness of proton moderated and proton reflected slab-shaped volumes of aqueous solutions of UO2F2 enriched to 93.2% in U235 were measured at chemical concentrations near that required for minimum critical volume. These data yield 1.76 ± 0.07 in. as the minimum critical thickness of an infinite slab of the materials of the experiment at a concentration of 532 g U235/l This result is compared with a three-group two-region analysis of the infinite slab.