Two experimental silos were evaluated: 1. Nylon evacuated bags, with the inlet of a heavy duty yacuum cleaner to 3.2 kg/cm2 and 2. P.V.C. tube with hand-compaction, with the objective of determining which is the most suitable and inexpensive for silage research. A 75% forage plants and 25o/o weed pasture was ensiled, with 25% DM. at the moment of ensiling. The forage was wilted to reach 29.5% and 32% D.M. After packing the silos, three different compaction pressures were applied: 0, 40 and 80 g/cm2, and then the silos were stored for 45 days. ln both silos, D.M. and total protein significantly decreased (P < 0,01) with respect to the original material, even more with no pressure. D.M. osses were higher in P.V.C. silos, reaching over 25%. Butyricacid was not found in any case; acetic acid and ammonia-nitrogen remained low. Lactic acid was within the normal range, being higher with the highest Ievels of D.M. (P < 0.01). Final grade of alI the silos was “very good”. pH was normal (4.0). Both types of silos were adequate to use in research, but the oxygen extraction by yacuum is very important, for fermentation studies in the aboratory.