Three different methods for the estimation ofin vitrofermentation kinetics are compared. The glass syringe, flow gasometer and pressure transducer methods were used for measurement of gas production. The rumen fluid from fistulated Merino sheep mixed with McDougall's buffer (1: 1) was used as an inoculum and added at an amount of 35 ml into the fermentation vessels containing 0.25 g of meadow hay. The total gas produced was recorded after 12, 24, 36, 48, 60, 72 and 96 h of incubation. Hay dry matter degradability was the same with all three methods and achieved 56.5 to 58.2%. Total volatile fatty acids were significantly lower with the pressure transducer method than with the syringe and flow gasometer method. Lower values of mol% of butyrate and valerate obtained with the flow gasometer and pressure transducer methods in comparison with the syringe were also observed. Total gas production estimated by the flow gasometer method was lower than that stated by the two other methods. With regard to precision of the used methods syringe method was the best followed by the pressure transducer and flow gasometer method. It can be concluded that in spite of some limitations the pressure transducer method used in this experiment can be regarded as suitable for total gas estimation inin vitrorumen fermentation experiments.