As a contribution to a required review of the American National Standard for Nuclear Criticality Safety in Operations with Fissionable Materials Outside Reactors, limits for homogeneous 235U systems have been recalculated to confirm their subcriticality or, where there were doubts, to propose more restrictive values. In addition, other limits were calculated to propose for inclusion in the Standard, namely limits for solutions of 235UO2(NO3)2 and limits for solutions of both UO2F2 and UO2NO3)2 that allow credit for the presence of 238U. Limits were also calculated for uranium oxides. The same three methods of calculation were used as in similar work done recently for plutonium systems. The validity of each was established by extensive correlations with pertinent critical experiments.