The fracture under internal pressure of twelve vessels working in the upper shelf region is analyzed by means of elasto-plastic criteria. The vessels were manufactured from steels with yield stresses ranging from 295 to 861 N/mm² and toughnesses between 4.1 and 9.2 kN/mm^3/2. The vessels were designed to operate at about σ_ys/1.5 and consequently had different thicknesses. Artificial defects were introduced in the base material and in the heat-affected zone. Some of the vessels were tested in the as-welded condition, some in the stress-relieved condition. Critical crack lengths ranged from 110 to 340 mm. The J_R method of Paris and a modified version of the two-parameter method of the Central Electricity Generating Board (United Kingdom) were applied. Predicted burst pressures are in good agreement with measured values, the J_R method yielding errors within the 3% range and the two-parameter method giving errors ranging from 3 to 8%, always on the conservative side.