Pressure cycle tests were performed on two types of Cr–Mo steel pressure vessels with notches machined on their inside under hydrogen-gas pressures, between 0.6 and 45 MPa at room temperature. Fatigue crack growth (FCG) and fracture toughness tests of the Cr–Mo steels samples from the vessels were also carried out in gaseous hydrogen. The Cr–Mo steels showed accelerated FCG rates in gaseous hydrogen compared to ambient air. The fracture toughness of the Cr–Mo steels in gaseous hydrogen was significantly smaller than that in ambient air. Four pressure vessels were tested with gaseous hydrogen. All pressure vessels failed by leak-before-break (LBB). The LBB failure of one pressure vessel could not be estimated by using the fracture toughness in gaseous hydrogen KIC,H; accordingly, the LBB assessment based on KIC,H is conservative and there is a possibility that KIC,H does not provide a reasonable assessment of LBB. In contrast, the fatigue lives of all pressure vessels could be estimated by using the accelerated FCG rates in gaseous hydrogen.