In the previous report, the authors developed a particular computer program based on the finite element method for theoretical analyses on buckling of web plates with slots for longitudinals. The authors also conducted several kinds of experiments and compared the results with those analyzed by the computer program. Quite good agreement was recognized between them. Subsequent to the previous report, the authors carried out systematic calculations on the buckling strength of web plates with slots for longitudinals and investigated the effect of reinforcement with collar plates, face plates around slots, horizontal stiffeners on web plates or partially increased thickness of web plates on shear buckling of web plates with slots. As the results, sufficient informations were obtained on the buckling strength of web plates. Finally, many design charts of the buckling strength of web plates with slots for longitudinals were made and presented here; they are considered to be very valuable for the design of such web plates. Furthermore, analyses with the design charts were conducted on buckling failures of web plates of transverse rings in an oil tanker. In the study, loading conditions in which actual failures in web plates possibly occured were examined and theoretical conditions in which the failures occured were ascertained.