The objective of this work was to evaluate three tropical forage species for their in vitro methane (CH₄) production and organic matter degradability, in order to determine the relationships between forage grass nutritive quality and CH₄ production. Guinea grass (Megathyrsus maximus), palisade grass (Urochloa brizantha), and signal grass (Urochloa decumbens) were evaluated. Palisade grass showed the highest organic matter, neutral detergent fiber, acid detergent fiber, lignin, and lower-crude protein content. Signal grass had the highest values for hemicellulose and neutral detergent fiber-nitrogen, and the lowest-cellulose content. Guinea grass and signal grass showed a higher-total gas production than palisade grass. Besides, Guinea grass showed an increased CH₄ production, and palisade grass showed lower value for truly degraded organic matter, and reduced partitioning factor, in comparison to signal grass. An increased CH₄ production was observed in cases of lower hemicellulose and paratitioning factor. The nutritive value and CH₄ production of forages may be employed as parameters, aiming at the sustainability of ruminant production.