Three Gram-stain-negative, obligately anaerobic, non-spore-forming, rod-shaped bacteria (strains YIT 12056T, YIT 12057T and YIT 12058T) were isolated from human faeces. These strains were characterized by phylogenetic analyses based on 16S rRNA gene sequence and phenotypic tests. 16S rRNA gene sequence analyses revealed that strains YIT 12056T, YIT 12057T and YIT 12058T were most closely related to the type strains of Bacteroides gallinarum, Bacteroides uniformis and Bacteroides intestinalis with approximate similarity values of 96.6, 95.0 and 96.7%, respectively. The DNA G+C contents of the novel strains were 45.3 (YIT 12056T), 45.2 (YIT 12057T) and 43.6 mol% (YIT 12058T) and the major respiratory quinones of all three isolates were menaquinones MK-10 and MK-11. These properties were typical for members of the genus Bacteroides. The results of the other phenotypic analyses also supported the affiliation of these strains to the genus Bacteroides. The 16S rRNA gene sequence analysis, analysis of the major cellular fatty acids and other biochemical tests enabled the genotypic and phenotypic differentiation of the three new strains. Based on these data, three novel species, Bacteroides clarus sp. nov., Bacteroides fluxus sp. nov. and Bacteroides oleiciplenus sp. nov. are proposed. The type strains of B. clarus, B. fluxus and B. oleiciplenus are YIT 12056T (=JCM 16067T=DSM 22519T), YIT 12057T (=JCM 16101T=DSM 22534T) and YIT 12058T (=JCM 16102T=DSM 22535T), respectively.