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This study appraised the effects of vegetable oils on in vitro methanogenesis, gas production, fatty acid composition and feed fermentation in buffaloes. Sesame (SOL) and mustard (MOL) oils were added individually to a basal diet of sorghum hay at the rate of 0, 0.4 and 0.8 ml per 30 ml of incubation fluid in 100 ml calibrated glass syringes. Rumen inoculums was obtained from four fistulated buffalo steers and incubated with 200 mg of substrate for 24 h at 39℃. Gas production was recorded by displacement of piston. Methane in the gas phase and volatile fatty acids in the fermentation medium were estimated by gas liquid chromatography. In vitro true degradability of dry matter (TDDM), neutral detergent fibre degradability (NDFD) was estimated, and microbial biomass production (MBP) and partitioning factor (PF) were calculated. Increasing doses of SOL and MOL linearly decreased (P<0.05) methane production without any variation between oil types. Both oils linearly decreased TDDM and NDF digestibility of feeds as well as MBP, however, the effects were more (P<0.05) pronounced with MOL. Acetate production was not affected (P>0.05), but increased production of propionate and butyrate and reduced (P<0.05) acetate to propionate ratio was evident with addition of oils. Mustard oil exerted greater (P<0.05) inhibitory effects on degradability and microbial biomass production at corresponding doses. Therefore, sesame oil is better than mustard oil as methane inhibiting agent without adversely affecting feed digestibility and may be considered as valuable feed supplement.