This study evaluated the potential of tropical forage species to improve nutrient use efficiency and reduce enteric methane emissions using the in vitro gas production technique. The objective was to assess digestibility and methane (CH₄) production of Brachiaria brizantha (Hochst. ex A. Rich.) Stapf and Inga edulis Mart., evaluated individually and in mixtures, as a strategy to enhance the sustainability of tropical livestock systems. Forages were incubated in vitro for 48 h, either alone or combined, and total gas production, dry matter degradation (DMD), and methane production were measured. Data were analyzed using a completely randomized block design. I. edulis showed a substantially higher crude protein content than U. brizantha (18.16 vs. 6.31%), while neutral detergent fiber (NDF) was also higher in I. edulis (78.88 vs. 67.28%). After 48 h of incubation, U. brizantha and the mixture containing 15% I. edulis produced the highest total gas volumes (179.33 and 175.04 mL/g DM, respectively), followed by the mixture with 30% inclusion (153.83 mL/g DM). In contrast, pure I. edulis showed the lowest gas production (31.46 mL/g DM). Significant differences in DMD were observed among treatments. At 24 h, U. brizantha showed the highest degradation (50.39%), followed by mixtures with 15% (49.10%) and 30% (44.88%) I. edulis, while the legume alone had the lowest value (14.03%). A similar pattern was observed at 48 h. Methane production at 24 h was highest in U. brizantha (5.45 mL/g DM), followed by mixtures with 15% (5.21 mL/g DM) and 30% (4.26 mL/g DM) I. edulis. Pure I. edulis produced negligible methane (0.03 mL/g DM). These results indicate that moderate inclusion (15%) of I. edulis maintains fermentative activity similar to that of the grass alone, while higher inclusion levels reduce gas production, dry matter degradation, and methane emissions.