The kinetic parameters of the dry matter and neutral detergent fiber degradation of some tropical forages were estimated through anaerobic incubations by the cumulative gas production technique and by curve subtraction. The measurements were made using a non-automated system, which has a manometer connected to a syringe. Corn silage and the forages Cynodon dactylon, Pennisetum purpureum, Brachiaria brizantha, Brachiaria decumbens, and Melinis minutiflora were studies. The kinetic interpretations of the cumulative gas production data were analyzed by using a multicompartmental logistic model. The data obtained with this system showed lowest coefficient of variation for both dry matter (DM) and neutral detergent fiber (NDF), especially after 12 h of incubation, being similar to those described in other studies with automated systems. A strong linear relationship was observed when the total of gas produced was plotted against the NDF degradation, the amount of neutral detergent soluble carbohydrate and the effective degradability of the forages studied. It was concluded that kinetic parameters of the rapid and slow fractions in the feed constituents could be estimated accurately by cumulative gas production measured with this cheaper non-automated system.