Circumferential ring stiffeners are commonly used to improve the buckling strength of cylindrical shells. Under special circumstances, stiffener ring needs to be partially cut in order to avoid interference with vessel attachments or surrounding structures. No clear guideline is available in rule-based method to deal with such case. This paper investigates the extent of reduction in buckling capacity for a range of cylindrical shell geometries with stiffener rings having different cross sections and different extents of circumferential cut. Finite-element (FE)-based analysis as per ASME Section VIII, Division 2, Part 5 has been employed to determine the permissible external pressure in each of the cases. Effects of ring cross section and extent of circumferential cut of stiffening ring on the maximum permissible external pressure have been presented. A total of 63 combinations of shell-stiffening ring configurations of different L/D, D/t ratios, cross section shape, and extent of cut have been investigated. Geometrical parameters for these combinations under study are so chosen that normal working range in industries is covered. The results obtained provide guidelines to design shells with partially cut stiffening rings.