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Nickel-based superalloys have attracted immense attention in the oil and gas industry due to their outstanding combination of mechanical properties and corrosion resistance. In corrosive service environment, hydrogen embrittlement is a severe issue. In the present work, the susceptibility of two precipitation-hardened nickel-based alloys, i.e., Alloy 718 and Alloy 725, to hydrogen embrittlement was studied using slow strain-rate tensile test and advanced characterization techniques. The mechanical properties and fracture behavior of these two alloys were compared in both hydrogen-free and hydrogen-charged conditions. In the presence of hydrogen, Alloy 718 failed prevalently through a combination of transgranular and intergranular cracking behavior, while Alloy 725 failed primarily through intergranular failure with a considerably lower resistance to hydrogen embrittlement. This distinction was attributed to their …