The study was carried out to determine the effect of lavender (Lavandula angustifolia) and peppermint (Mentha piperita) essential oils (EO) (0, 1.5 and 3.0 mu l/ml) on fermentation, digestibility, gas and methane production of feed with Buffalo rumen liquor. The study was performed with alfalfa and concentrate mixture (60:40) as a substrate and two buffalo was used as inoculum for rumen fluid in in vitro gas production. As a result, gas production was increased with supplementation of 1.5 mu l/ml lavender and peppermint EO oil but decreased supplementation of 3.0 mu l/ml (P<0.0) at 24 h after incubation. The methane production was decreased with lavender EO (P<0.01) as decreased by 45.57, 23.59 and 16.54 mL/g at 0, 1.5 and 3.0 mu l/ml of lavender EO, respectively. There was a decrease in in vitro methane production (%) with high levels of peppermint oil (P<0.05) but gas production was decreased with a high dose (3.0 mu l/ml). In the present study in vitro true dry matter digestibility (TDMD) and organic matter digestibility decreased with high doses supplementation of lavender and peppermint oil (P<0.01). Lavender EO had no effect on rumen volatile fatty acids production and pH (P>0.05). Rumen pH was not affected with lavender and peppermint EO supplementation (P>0.05), that changed within normal range of rumen pH (6.5 to 7.0). Ruminal acetate production was increased, and propionate and butyrate production were decreased with 3.0 mu l/ml peppermint EO supplementation. Lavender EO was more effective for reduction of methane production without negative effects (especially gas production and TDMD) but this effect becomes negative effects at higher doses of EO supplementations. So, lavender and peppermint EO could be need more study as a feed additive to reduce methanogenesis in in vivo experiments.