The aim of the present paper was to study the fermentation characteristics and kinetics of the carbohydrate fractions of fresh, ensiled and hay of oats (Avena sativa) using the Cornell Net Carbohydrate and Protein System (CNCPS) and the in vitro gas production technique (GPT). The whole forage and its NDF and EIR (ethanol insoluble residue) fractions were incubated in order to estimate the fermentation kinetics of carbohydrate fractions (A, B1 and B2) with the curve subtraction method. The carbohydrates fermentation kinetics estimated with the GPT agree with the three CNCPS carbohydrate fractions and explain some modification due to forage preservation methods. For all forages, the fermentation rate of the three CNCPS carbohydrate fractions showed the same ranking A > B1 > B2. Fermentation rate value (RM: 0.163, 0.057, 0.032 h-1 A, B1, B2 fraction for fresh oats; 0.106, 0.032, 0.016 h-1 for A, B1, B2 fractions of ensiled oats; 0.165, 0.051, 0.022 h-1 A, B1, B2 fraction for oats hay) could be used as kd in the CNCPS.