Methanomassiliicoccales are rare members of the human gut microbiota. Scatterplots of the genera (A) “Ca. Methanomethylophilus” and (B) Methanomassiliicoccus show that their prevalence and mean abundance is low across most studies and populations (35 data sets) with subjects (n = 4,472) from Austria (AUT), China (CHN), Denmark (DNK), Ethiopia (ETH), Fijo (FJI), Great Britain (GBR), Ghana (GHA), Israel (ISR), Madagascar (MDG), Mongolia (MNG), The Netherlands (NDL), El Salvador (SLV), Sweden (SWE), Tanzania (TZA), and the United States (USA).