This research was conducted to evaluate effects of a Yucca schidigera extract (YSE) on 24h in vitro rumen fermentation and methane production of diets with various forage:concentrate ratios. Experimental treatments were alfalfa (Medicago sativa), fescue (Festuca arundinacea) orchard grass (Dactylis glomerata), Bermuda (Cynodon dactylon)and switch grass (Panicum virgatum) plus 0 or 110g/kg of YSE in a 1.0 forage diet (Exp. 1), a medium forage diet (forage:concentrate=0.5:0.5; Exp. 2), and a low forage diet (forage:concentrate=0.1:0.9; Exp. 3). Two ruminally-fistulated steers consuming 0.7 alfalfa hay and 0.3 concentrate were used as rumen fluid donors. Gas emission from each fermentation vessel was measured continuously by an automated pressure transducer system. YSE did not affect pH, 24h pressure, gas production, maximum pressure, degradation rate, lag time, or total and individual VFA concentration in all forage, medium forage, and low forage diets. YSE addition decreased (P<0.05) methane production at 24h. There were no interactions between YSE and forage source and diet forage:concentrate ratio. Results suggest that YSE has the potential to reduce methane production in ruminants across a wide range of forages fed in diets with different forage:concentrate ratios.