To avoid failures due to hydrogen embrittlement, it is important to know the amount of hydrogen absorbed by certain steel grades under service conditions. When a critical hydrogen content is reached, the material properties begin to deteriorate. The hydrogen uptake and embrittlement of three different carbon steels (API 5CT L80 Type 1, P110 and 42CrMo4) was investigated in autoclave tests with hydrogen gas (H₂) at elevated pressure and in ambient pressure tests with hydrogen sulfide (H₂S). H₂ gas with a pressure of up to 100 bar resulted in an overall low but still detectable hydrogen absorption, which did not cause any substantial hydrogen embrittlement in specimens under a constant load of 90% of the specified minimum yield strength (SMYS). The amount of hydrogen absorbed under conditions with H₂S was approximately one order of magnitude larger than under conditions with H₂ gas. The high hydrogen content led to failures of the 42CrMo4 and P110 specimens.