An investigation of the Crack Tip Opening Displacement (CTOD) fracture behavior of four pressure vessel steels and one ship steel has been conducted.The purpose of the investigation was to determine the fracture behavior of the steels, to study the effects of CTOD testing variables, to examine various methods of evaluating test records, and to study the relationships among several fracture toughness parameters.The five steels studied (A508, A533, A516, A517, and A131) had yield strengths from 240 MPa to 750 MPa. In addition, three specimen sizes of the A533 and A516 steels were studied.