This supplementary material supports the study "Manganese- and Iron-Dependent Marine Methane Oxidation." The research investigates the role of manganese and iron in marine methane oxidation, using sediment samples from the Eel River Basin. Sediment samples were collected from two cruises and used in experiments with different electron acceptors, including manganese compounds, iron compounds, and sulfate. Artificial sulfate-free seawater was prepared and used in the incubations, with methane added to the headspace. Isotope analysis was performed to track methane oxidation. Free energy calculations were conducted to determine the thermodynamic feasibility of methane oxidation using manganese and iron. The in situ conditions for these calculations were based on measured concentrations of various ions and compounds. Dissolved manganese and iron were measured using specific analytical techniques, and clone libraries were used to analyze the microbial communities involved in methane oxidation. The study also discusses additional sources of manganese and iron to the Eel River Basin, including aeolian dust and hydrothermal activity. It highlights the potential for these metals to oxidize methane, even though their contribution may be smaller than riverine inputs. The presence of dissolved manganese in incubations was observed, but it was expected that much of it would precipitate as manganese carbonates. The supplementary figures and legends provide additional information on the microbial communities and phylogenetic relationships of the bacteria involved in methane oxidation. The references list the sources of the methods and data used in the study.This supplementary material supports the study "Manganese- and Iron-Dependent Marine Methane Oxidation." The research investigates the role of manganese and iron in marine methane oxidation, using sediment samples from the Eel River Basin. Sediment samples were collected from two cruises and used in experiments with different electron acceptors, including manganese compounds, iron compounds, and sulfate. Artificial sulfate-free seawater was prepared and used in the incubations, with methane added to the headspace. Isotope analysis was performed to track methane oxidation. Free energy calculations were conducted to determine the thermodynamic feasibility of methane oxidation using manganese and iron. The in situ conditions for these calculations were based on measured concentrations of various ions and compounds. Dissolved manganese and iron were measured using specific analytical techniques, and clone libraries were used to analyze the microbial communities involved in methane oxidation. The study also discusses additional sources of manganese and iron to the Eel River Basin, including aeolian dust and hydrothermal activity. It highlights the potential for these metals to oxidize methane, even though their contribution may be smaller than riverine inputs. The presence of dissolved manganese in incubations was observed, but it was expected that much of it would precipitate as manganese carbonates. The supplementary figures and legends provide additional information on the microbial communities and phylogenetic relationships of the bacteria involved in methane oxidation. The references list the sources of the methods and data used in the study.