Organic matter (OM) degradation of 21 feedstuffs was investigated with rumen fluid using a rumen in situ technique and a gas production technique. Fitting the nylon bag data to an exponential model showed that there was a high variation in the rate of OM degradation ranging from 1.7% h-1 for protected solvent extracted soybean meal to 10.5% h-1 for potato pulp. The percentage fermentable OM (FOM), calculated from the nylon bag data, ranged from 26.9% for maize gluten meal to 76.4% for pea meal. Gas production was recorded with fully automated equipment using twice-diluted rumen fluid. The gas production profiles were fitted to a mono-phasic and a tri-phasic model. The aim of the study described is to investigate the possibilities to estimate in situ degradation characteristics using gas production characteristics and chemical composition. The in situ washout fraction (W), degradable fraction (D) and undegradable fraction (U) could be predicted from chemical composition and gas production parameters with R2 ranging from 0.50 to 0.72. There was a closer relationship between in situ degradation rate of OM (kd) and the incubation period halfway to maximum gas production (B), using the tri-phasic model (R2 = 0.58) than the mono-phasic model (R2 = 0.43). Accounting for an in situ lag-period slightly improved prediction of kd by gas production parameters (R2 = 0.47-0.62). Percentage FOM, calculated from in situ results, could be predicted from chemical composition and gas production parameters with R2 ranging from 0.50 to 0.75. Transformation of kd (determined in situ) to its half-life value of degradation ((ln 2/kd) × 100) provided a slight improvement of kd prediction by chemical composition and gas production parameters, with R2 ranging from 0.56 to 0.81. There was only a moderate relationship for OM degradation in these feedstuffs determined using an in situ and a gas production technique. © 2002 Elsevier Science B.V. All rights reserved.