This study characterised 16 tropical perennial grass species in terms of in vitro methane output and related their digestibility and rumen fermentation with methane output. The grass samples were collected, dried in a forced oven, and ground and analysed for nutrient composition. In vitro gas production and organic matter digestibility (IVOMD) were determined using rumen fluid collected, strained and anaerobically prepared. A semi-automated system was used to measure gas production through in vitro incubation at 39°C. Anthephora argentea and Stipagrostis ciliate produced the highest concentration of methane in terms of g kg^–1 digestible dry matter (DDM) and g kg^–1 digestible organic matter (IVOMD). Cenchrus ciliaris, Setaria verticillata and Panicum coloratum produced the lowest (P < 0.05) methane when expressed in terms of g kg^–1 DDM and g kg^–1 IVOMD. Ash, ether extract, non-fibrous carbohydrate, neutral and acid detergent insoluble nitrogen, and crude protein were negatively correlated with methane production. Methane production positively correlated with neutral and acid detergent fibre, cellulose and hemicellulose. It is important to focus on screening and selecting perennial grass with higher nitrogen content and low methane production to mitigate methane production under tropical conditions.