The objective of this study was to determine the effect of stage of growth and ensiling on in vitro gas production (GP) of fresh and ensiled whole-crop oats. Oats (Avena Sativa L. cv Cantara) were harvested and ensiled at six growth stages (GS):boot (GS 45), heading (GS 59), water ripe (GS 69), early milk GS 73), early dough (GS 83) and grain ripe (GS 91) according to Zadoks´ decimal code. The crop was established at the experimental station of INIA-La Estanzuela (Colonia, Uruguay, 34°20?S, 57°41?W).