Summary Anaerobic methane‐oxidizing archaea (ANME) are known to play an important role in methane flux, especially in marine sediments. The 16S rRNA genes of ANME have been detected in terrestrial freshwater subsurfaces. However, it is unclear whether ANME are actively involved in methane oxidation in these environments. To address this issue, Holocene sediments in the subsurface of the Kanto Plain in Japan were collected for...

Summary The methanogenic communities and pathways in a high‐temperature petroleum reservoir were investigated through incubations of the production water and crude oil, combined with radiotracer experiments and molecular biological analyses. The incubations were conducted without any substrate amendment and under high‐temperature and pressurized conditions that mimicked the in situ environment (55°C, 5 MPa). Changes in methane...