This report attempts to summarize the status of nuclear pressure vessel operating parameters, and is addressed particularly to vessel fabricators and to committees charged with framing pertinent specifications.Although there are several different types of nuclear reactors, based on the type of cooling medium used, license to confine this report to aqueous type reactors is taken for two practical reasons: (1) the problems peculiar to vessels containing high pressures under conditions of neutron irradiation have particular significance and urgency at this stage of reactor development, and (2) water-cooled reactors to date have the benefit of the acquisition of more operational history than other types.