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Abstract Recently, room temperature superconductivity was measured in a carbonaceous sulfur hydride material whose identity remains unknown. Herein, first-principles calculations are performed to provide a chemical basis for structural candidates derived by doping H₃S with low levels of carbon. Pressure stabilizes unusual bonding configurations about the carbon atoms, which can be six-fold coordinated as CH₆entities within the cubic H₃S framework, or four-fold coordinated as methane intercalated into the H-S lattice, with or without an additional hydrogen in the framework. The doping breaks degenerate bands, lowering the density of states at the Fermi level (N_F), and localizing electrons in C-H bonds. Low levels of CH₄doping do not increaseN_Fto values as high as those calculated for$$Im\bar{3}m$$ $Im\overline{3}m$-H₃S, but they can yield a larger logarithmic average phonon frequency, and an electron–phonon coupling parameter comparable to that ofR3m-H₃S. The implications of carbon doping on the superconducting properties are discussed.