This study was initiated to evaluate the potential of near infrared reflectance (NIR) spectroscopy to predict in vitro gas production parameters of botanically complex herbage samples. A total of 94 herbage samples harvested in natural meadows located in the mountains near Le´on in Northwest Spain were analyzed to determine their chemical composition. In addition, all herbage samples were incubated in vitro in buffered rumen fluid to determine fermentation kinetics using a gas production technique, and scanned in a spectrophotometer to obtain NIR spectra. Prediction equations showed that NIR spectra could explain a high proportion of the variability (R2 >0.94) related to some in vitro gas production parameters (e.g., fractional rate of fermentation (c) and